Step-by-Step Instructions Step 1 — Prepare Your Pan and Preheat the Oven

Preheat your oven to 350°F (175°C). Line a 9×13-inch glass or ceramic baking pan with parchment paper, leaving an overhang on two sides. This makes it easy to lift the bars out later. Lightly grease the pan so the parchment stays in place.

Step 2 — Make the Buttery Shortbread Crust

In a food processor, pulse the flour, powdered sugar, cornstarch, and salt together. Add the cold butter cubes and pulse until the mixture resembles coarse crumbs — about 10 to 15 short pulses. When you squeeze a handful, it should just hold together. If you don’t have a food processor, you can use your fingertips to rub the butter into the dry ingredients.

Transfer the mixture into your prepared pan and press it firmly and evenly into the bottom. Use the bottom of a measuring cup to compact it, paying special attention to the corners. Refrigerate the crust for 20–30 minutes — this is the secret to keeping it from puffing up during baking.

Step 3 — Blind Bake the Crust

Bake the chilled crust for 18–22 minutes, until the edges are just starting to turn golden. You don’t need deep color — a light bake is all you want here, as it will go back in the oven with the filling.

Step 4 — Prepare the Lemon Filling

While the crust bakes, prepare your filling. In a large bowl, whisk the eggs and granulated sugar together until combined. Add the flour a little at a time, whisking vigorously to prevent lumps. Pour in the fresh lemon juice and add the lemon zest and a pinch of salt. Whisk everything together until smooth and uniform.

Step 5 — Bake the Lemon Bars

As soon as the crust comes out of the oven, pour the lemon filling directly over it while it is still hot. This is important — pouring filling onto a warm crust helps the layers bond. Immediately return the pan to the oven and bake for another 28–32 minutes, until the top is set and no longer jiggles in the center.

Step 6 — Cool and Chill

Remove from the oven and allow to cool completely at room temperature, at least 1 hour. Then cover and refrigerate for a minimum of 2 hours (overnight is even better). The filling needs this time to fully set.

Step 7 — Slice and Serve

Lift the bars out of the pan using the parchment overhang. Place on a cutting board. Using a sharp knife, cut into bars — wipe the blade clean between each cut for neat edges. Dust generously with powdered sugar just before serving and top with thin lemon slices if desired.