Prep your pan and oven. Heat the oven to 350°F (175°C). Line a 9x13-inch baking pan with parchment, leaving overhang on two sides for easy lifting. Lightly grease the parchment and exposed sides.

Make the shortbread crust. In a large bowl, cream the butter and sugar until smooth and slightly fluffy. Add the flour and salt. Mix just until a soft, crumbly dough forms. Do not overmix.

Press and par-bake. Press the dough evenly into the prepared pan, going all the way to the edges and corners. Use the bottom of a measuring cup to level and compact. Bake for 18–20 minutes, or until the edges are lightly golden. Leave the oven on.

Whisk the filling. In a medium bowl, whisk the eggs and sugar until combined and a bit pale. Whisk in the flour and salt until smooth. Stir in the lemon juice and zest. The mixture should be glossy and lump-free.

Pour onto hot crust. While the crust is still hot, pour the lemon mixture over it. This helps the filling set quickly and prevents the crust from lifting or floating.

Bake to set. Return the pan to the oven and bake 18–22 minutes, or until the center no longer jiggles and the top looks set with tiny bubbles. A few small surface bubbles are normal.

Cool completely. Let the bars cool in the pan on a rack for 1–2 hours, then chill for at least another hour. Cooling ensures clean slices and a creamy texture.

Finish and slice. Lift the slab out using the parchment. Dust generously with powdered sugar. Use a sharp knife to cut into 20–24 squares, wiping the blade between cuts for neat edges.