Preheat oven to 350 degrees F. Line a 9x13 ceramic or glass pan with parchment paper with overhang. No need to grease it.
In a large bowl, whisk flour, sugar, and salt until well combined. Cut in the cubes of VERY cold butter into this mixture using a pastry blender or use your fingers (but be quick so the butter stays cold!), until the flour mixture is incorporated into the butter and you get pea size crumbles or smaller.
Press down the mixture into the prepared pan on all sides using something like a measuring cup. Make sure it's compact and evenly distributed.
Bake about 20 minutes until golden brown around the edges. Then, remove from oven and press down the crust slightly using a spoon to make it compact (some parts may have expanded with the heat).
While the crust is baking, whisk together flour and sugar in a large bowl. In a separate bowl, whisk 6 eggs plus the egg yolk until combined, and add it to the flour and sugar mixture. Mix until combined. Add lemon juice and lemon zest and mix until well-combined and incorporated.
Pour filling onto prepared crust. Bake for 20-25 minutes until the filling is set.
Allow to cool in the pan for at least 3 hours. You can also refrigerate it overnight for firmer texture (highly recommended). Remove from pan, cut into squares and dust with confectioner's sugar. Enjoy!