Preheat the oven to 350°F (175°C) and butter a 23x33 cm baking dish.
Brown the breakfast sausage in a large skillet over medium heat, breaking it into bite-sized pieces. Remove sausage with a slotted spoon, leaving 2 tablespoons of fat in the pan.
Add diced onion and chopped bell pepper to the skillet with sausage drippings and sauté for 4 to 5 minutes until softened. Stir in minced garlic during the last minute.
Spread thawed hashbrowns evenly in the prepared baking dish and season lightly with salt and pepper.
Top hashbrowns with the cooked sausage and vegetable mixture.
Whisk together eggs, milk, softened cream cheese, salt, black pepper, paprika, and cayenne pepper if using, until smooth.
Pour the egg mixture evenly over the hashbrown and sausage layers. Gently press with a fork to allow liquid penetration.
Sprinkle shredded cheddar cheese evenly on top.
Bake uncovered for 45 to 50 minutes until the center is set and the top is golden brown. Edges should slightly pull away from the dish.
Check doneness by inserting a clean knife in the center; it should come out clean.
Serve garnished with fresh chives or green onions, sour cream, and hot sauce or salsa as desired.