Preheat and prep: Preheat your oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper, leaving a little overhang so you can lift the bars out later.

Make the crust: In a medium bowl, stir together melted butter, sugar, flour, and salt until it forms a soft dough. Press it evenly into the bottom of your prepared pan—use your hands or the bottom of a flat cup to get it smooth and even.

Bake the crust: Pop it in the oven and bake for 18–20 minutes, or until it’s just starting to turn golden around the edges. Remove and set aside while you prep the filling.

Whisk the filling: In a large bowl, whisk together the sugar and flour. Add the eggs, lemon juice, and zest, and whisk until smooth. It should be pale yellow and glossy—no lumps allowed.

Bake again: Pour the filling over the warm crust. Return the pan to the oven and bake for another 20–22 minutes, or until the center is set and no longer jiggles.

Cool and chill: Let the bars cool completely at room temperature, then chill in the fridge for at least 2 hours (overnight is even better). This helps the filling set and makes them easier to slice.

Dust and slice: Just before serving, dust generously with powdered sugar. Slice into neat squares or rectangles, and prepare to wow your tastebuds.