Sweet Potato Cranberry Gratin

Name: Sweet Potato Cranberry Gratin
Prep time: 30 min
Cook time: 1 h 30 min
Total time: PT-492126H9M52S
Ingredients: 3-4 lbs sweet potatoes (about 5-6 medium), peeled and sliced 1/8-inch thick (use a mandoline if you have one); 3/4 cup dried cranberries (not Craisins—get the good unsweetened ones if possible); 1 medium yellow onion, thinly sliced; 3 cloves garlic, minced; 2 tablespoons fresh thyme leaves (or 2 tsp dried); 1 tablespoon fresh rosemary, minced (or 1 tsp dried); Salt and freshly cracked black pepper; 2 cups heavy cream; 1/2 cup whole milk; 2 tablespoons unsalted butter; 2 tablespoons all-purpose flour; 3/4 teaspoon salt; 1/2 teaspoon black pepper; 1/4 teaspoon nutmeg (secret weapon); Pinch of cayenne pepper (optional but adds warmth); 1 cup Gruyère cheese, shredded (or sharp white cheddar—don’t skip the cheese); 3/4 cup panko breadcrumbs; 1/2 cup pecans, chopped; 3 tablespoons unsalted butter, melted; 2 tablespoons fresh parsley, chopped; Salt and pepper to taste; Mandoline slicer (highly recommended for even slices); 9×13-inch baking dish (preferably ceramic or glass); Large saucepan; Large bowl; Whisk; Sharp knife; Aluminum foil

By Tyla | Last modified on Nov 27, 2025

Featured in: Dinner

Listen, I know you came here thinking this was just another sweet potato casserole with marshmallows. WRONG. This is a legitimate, grown-up, sophistication-in-a-baking-dish gratin that happens to combine caramelized sweet potatoes, tart dried cranberries, a ridiculous amount of cream and cheese, and a crunchy pecan-breadcrumb topping that’ll make you weep with joy. We’re talking layers of thinly sliced sweet potatoes swimming in a garlicky, herb-infused cream sauce, studded with jewel-like cranberries, topped with nutty Gruyère and a buttery crumb situation that gets golden and crispy in all the right ways. This is the side dish that upstages the main course, the one that has your mother-in-law asking for the recipe, the one that makes people suddenly “too full for dessert” because they went back for seconds and thirds. I brought this to Thanksgiving once and my uncle literally proposed to it. Someone scraped the dish so thoroughly they almost took the enamel off. This gratin has MAIN CHARACTER ENERGY.

Why This Gratin Will Ruin All Other Sweet Potato Dishes Forever

Actually elegant. No marshmallows, no brown sugar overdose—just sophisticated, layered flavors that belong on a fancy restaurant menu.

Perfectly balanced. The sweetness of the potatoes is cut by tart cranberries, savory cream, nutty cheese, and aromatic herbs. It’s complex without trying too hard.

That texture though. Creamy, tender sweet potatoes with pockets of chewy-sweet cranberries and a crunchy, golden topping. Every bite is different.

Make-ahead magic. Assemble this the day before, pop it in the oven when guests arrive. Zero stress, maximum impressiveness.

Feeds a crowd. One 9×13 pan serves 8-10 people easily, and it’s substantial enough to be a main dish for vegetarians.

Holiday showstopper. This looks STUNNING on the table—those orange layers, ruby cranberries, golden crust. Pure autumn/winter vibes.

The Ingredients That Make the Magic

For the Sweet Potato Layers:

3-4 lbs sweet potatoes (about 5-6 medium), peeled and sliced 1/8-inch thick (use a mandoline if you have one)
3/4 cup dried cranberries (not Craisins—get the good unsweetened ones if possible)
1 medium yellow onion, thinly sliced
3 cloves garlic, minced
2 tablespoons fresh thyme leaves (or 2 tsp dried)
1 tablespoon fresh rosemary, minced (or 1 tsp dried)
Salt and freshly cracked black pepper

For the Cream Mixture:

2 cups heavy cream
1/2 cup whole milk
2 tablespoons unsalted butter
2 tablespoons all-purpose flour
3/4 teaspoon salt
1/2 teaspoon black pepper
1/4 teaspoon nutmeg (secret weapon)
Pinch of cayenne pepper (optional but adds warmth)

For the Topping:

1 cup Gruyère cheese, shredded (or sharp white cheddar—don’t skip the cheese)
3/4 cup panko breadcrumbs
1/2 cup pecans, chopped
3 tablespoons unsalted butter, melted
2 tablespoons fresh parsley, chopped
Salt and pepper to taste

Equipment You’ll Need:

Mandoline slicer (highly recommended for even slices)
9×13-inch baking dish (preferably ceramic or glass)
Large saucepan
Large bowl
Whisk
Sharp knife
Aluminum foil

Let’s Build This Masterpiece

Step 1: Prep Your Potatoes (The Foundation)

Preheat your oven to 375°F (190°C). Butter or spray a 9×13-inch baking dish generously.

Peel the sweet potatoes and slice them into 1/8-inch thick rounds. Consistency is KEY here—use a mandoline if you have one or take your time with a sharp knife.

If your slices are uneven, the thin ones will burn while the thick ones stay raw. We’re aiming for perfectly tender, evenly cooked layers.

Place the sliced sweet potatoes in a large bowl of cold water to prevent browning while you prep everything else. They can hang out there for up to an hour.

Thinly slice your onion and mince your garlic. Strip the thyme leaves off their stems. Get your herbs ready.

Step 2: Make the Cream Sauce (The Soul of This Dish)

In a medium saucepan over medium heat, melt 2 tablespoons butter until foamy.

Add the minced garlic and cook for 30 seconds until fragrant but not browned. Burnt garlic = bitter sadness.

Whisk in the flour and cook for 1-2 minutes, stirring constantly, until it forms a paste (this is a roux—fancy French cooking technique).

Gradually pour in the heavy cream and milk, whisking constantly to prevent lumps. Keep whisking until smooth.

Add salt, pepper, nutmeg, and cayenne. Bring to a gentle simmer, whisking frequently.

Let it simmer for 3-4 minutes until it thickens slightly—it should coat the back of a spoon.

Remove from heat and stir in the thyme and rosemary. Taste and adjust seasoning. It should taste rich, creamy, and well-seasoned.

Set aside while you assemble. The sauce will thicken more as it sits—that’s normal.

Step 3: Assemble the Layers (Like You’re Building a Delicious Tower)

Drain the sweet potato slices and pat them dry with paper towels or a clean kitchen towel. Excess water = soggy gratin.

Start layering in your buttered baking dish:

First layer: Arrange about 1/3 of the sweet potato slices in overlapping rows, covering the bottom. They should overlap like shingles on a roof.

Sprinkle with 1/3 of the sliced onions, 1/4 cup cranberries, a pinch of fresh herbs, salt, and pepper.

Pour about 1/3 of the cream sauce over the layer, making sure it seeps into all the cracks.

Sprinkle with about 1/3 cup of shredded Gruyère.

Second layer: Repeat with another 1/3 of sweet potatoes, onions, cranberries, herbs, cream sauce, and cheese.

Third layer: Final layer of sweet potatoes, remaining onions, cranberries, and cream sauce. Don’t add the last of the cheese yet—save it for the topping.

Press down gently with a spatula to compact the layers and make sure the cream mixture covers everything. If potatoes are peeking out, they’ll burn.

Step 4: Make the Crunchy Topping (The Showstopper)

In a medium bowl, combine panko breadcrumbs, chopped pecans, remaining Gruyère cheese, melted butter, and chopped parsley.

Season with a pinch of salt and pepper. Mix until the breadcrumbs are evenly coated with butter.

The mixture should look like wet sand and clump together slightly.

Taste a pinch (yes, raw breadcrumbs are fine). Adjust seasoning if needed.

Sprinkle this glorious mixture evenly over the top of the gratin, covering all the sweet potatoes completely.

The topping should be generous—don’t be shy. This is what gets golden and crispy and makes people lose their minds.

Step 5: Bake Low and Slow (Patience = Perfection)

Cover the baking dish tightly with aluminum foil. This traps steam and helps the potatoes cook through without the top burning.

Bake covered at 375°F for 45 minutes. The potatoes should be starting to soften.

Remove the foil and continue baking uncovered for another 30-40 minutes until:

The sweet potatoes are completely tender when pierced with a knife
The cream is bubbling around the edges
The topping is deeply golden brown and crispy
The cranberries are plump and jammy

If the top is browning too fast but the potatoes aren’t tender yet, tent loosely with foil and continue baking.

If the top isn’t browning enough, pop it under the broiler for 2-3 minutes at the end. Watch it like a hawk—broilers are aggressive.

Step 6: Rest and Serve (The Hardest Part)

Remove from the oven when it’s bubbling, golden, and gorgeous. It will smell INSANE.

Let it rest for 15-20 minutes before serving. This is CRUCIAL. If you dig in immediately, it’ll be a molten, soupy mess.

As it rests, the cream sauce thickens, the layers set, and it becomes slice-able instead of spoon-able.

Use a large serving spoon to scoop out portions, making sure each serving gets layers, cranberries, and that crispy top.

Watch as people take their first bite and immediately go silent because their mouth is too busy experiencing joy.

How to Serve This Show-Stopping Side

Thanksgiving Table: This goes with turkey, ham, prime rib—literally any main protein.

Holiday Dinner: Christmas, Easter, Friendsgiving—anytime you want to impress.

Vegetarian Main: Serve larger portions with a big green salad and crusty bread for a complete meal.

Brunch Situation: This works beautifully for a fancy brunch alongside eggs and bacon.

Make-Ahead and Storage Magic

This is THE ultimate make-ahead holiday side. Here’s how:

The Night Before:

Assemble the entire gratin through Step 4 (with topping)
Cover tightly with foil and refrigerate
Bring to room temp for 30 minutes before baking
Add 10-15 minutes to the covered baking time since it’s cold

Two Days Ahead:

Slice sweet potatoes and store in water in the fridge
Make the cream sauce and refrigerate
Prep the topping and store separately
Assemble the morning of or night before

Reheating:

Cover with foil and reheat at 350°F for 20-25 minutes
Uncover for last 5 minutes to re-crisp the top

Storage:

Refrigerate leftovers covered for up to 4 days
Reheat individual portions in microwave or oven
The flavors actually improve on day 2

Freezing:

Assemble but don’t bake, wrap tightly, freeze for up to 2 months
Thaw overnight in fridge before baking
Not recommended to freeze after baking—the texture gets weird

Why This Is Actually Genius

Let me break down the science behind the deliciousness:

Thin slicing ensures even cooking and maximum surface area for the cream to cling to.

The roux-based cream sauce thickens perfectly during baking without breaking or curdling.

Nutmeg enhances the natural sweetness of the potatoes without making it taste like a dessert.

Cranberries provide tart pops that cut through the richness and prevent sweet-potato-overload.

Gruyère melts beautifully and adds nutty, savory depth without overpowering.

Layering cheese throughout creates pockets of melted goodness instead of just a top layer.

The breadcrumb-pecan topping adds textural contrast and prevents the dish from being one-note creamy.

Resting time allows the starches to reabsorb liquid, transforming it from soupy to slice-able.

Covered baking steams the potatoes tender while protecting the topping from burning.

When to Make This Masterpiece

Thanksgiving: Obviously. This is peak Thanksgiving energy.

Christmas Dinner: Festive colors, elegant presentation, crowd-pleasing flavors.

Easter Brunch: Light enough for spring, impressive enough for a holiday.

Friendsgiving: Show up with this and become everyone’s favorite friend.

Fancy Dinner Party: When you want to seem like a culinary genius with minimal effort.

Sunday Supper: Make it on a lazy Sunday and eat the leftovers all week.

Potluck MVP: This travels well and serves a crowd—instant potluck winner.

Troubleshooting (When Things Go Sideways)

Q: My potatoes are still hard but the top is burning.
A: Cover with foil and keep baking. Your slices were too thick or oven temp is too high. Next time, slice thinner.

Q: It’s too watery/soupy.
A: You didn’t let it rest long enough, or you used too much liquid. Let it sit for 20-30 minutes to thicken up.

Q: The cream curdled.
A: The heat was too high or you didn’t whisk constantly. The roux prevents this, but if your oven runs hot, reduce temp to 350°F.

Q: The top didn’t get crispy.
A: Too much foil time or not enough butter in the topping. Broil for 2-3 minutes at the end.

Q: Can I use regular potatoes instead?
A: You can, but it won’t be the same dish. The sweetness of sweet potatoes is essential. Try a mix of both?

Q: My cranberries are rock-hard.
A: Soak them in warm water or orange juice for 10 minutes before using to plump them up.

Q: Can I skip the cheese?
A: You can, but it won’t be as rich. The cheese adds essential flavor and helps bind everything.

Q: It’s too sweet.
A: Add more salt, pepper, and herbs. Use unsweetened cranberries and don’t add extra sugar.