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

Make the crust: In a bowl, cream the butter and sugar until smooth and slightly fluffy. Add the salt, then mix in the flour just until the dough comes together. It should feel soft, not sticky.

Press and par-bake: Press the dough evenly into the prepared pan, building a subtle 1/2-inch lip around the edges. Prick the surface lightly with a fork. Bake 18–20 minutes, until the edges are lightly golden. Set aside.

Whisk the filling: In a medium bowl, whisk the sugar and flour to break up any lumps. Add the eggs and whisk until smooth but not foamy. Whisk in the lemon juice, zest, and salt. The mixture should be silky and bright.

Pour and bake: Give the filling one last stir, then pour it over the warm crust. Return to the oven and bake 20–24 minutes, until the center is just set and no longer jiggly. The surface may look matte with tiny bubbles—that’s fine.

Cool completely: Let the bars cool in the pan on a rack to room temperature, then refrigerate at least 2 hours. Chilling helps the filling set and makes cleaner slices.

Slice and finish: Use the parchment to lift the slab onto a cutting board. Dust lightly with confectioners’ sugar, then slice into 20–24 bars. Wipe the knife between cuts for neat edges.