For the crust: Preheat the oven to 350 degrees F. Grease a 9-by-13-inch pan with butter. If you want a thicker crust, use a 9x9 pan instead.
Stir together the flour, sugar, and salt. Add the butter to the bowl and use a pastry cutter to cut it all together until the mixture resembles fine crumbs.
Press into the prepared pan and bake until golden around the edges, about 20 minutes.
For the filling: Stir together the sugar and flour. Crack in the eggs and whisk to combine.
Add the lemon zest and juice and mix until combined. Pour over the crust and bake for 20-30 minutes or until the lemon filling doesn't jiggle.
Allow to cool in the fridge for a minimum of 2 hours, then sift powdered sugar over the top before cutting into squares.
Store leftover lemon bars in the fridge.
