Preheat your oven to 350 degrees F and line an 8×8-inch baking pan with parchment paper.
In the bowl of an electric mixer, add butter and powdered sugar. Beat together until pale and fluffy, about 3 minutes.
Add 1 cup of all-purpose flour and kosher salt. Mix until the dough comes together. It may look crumbly initially.
Firmly press the dough into the bottom of the prepared pan evenly.
Bake the crust for about 20 minutes until lightly browned.
In a clean mixing bowl, combine granulated sugar and eggs. Beat until smooth and creamy, about 2 minutes.
Add in fresh lemon juice and lemon zest. Stir to combine gently.
Fold in the 2 tablespoons of all-purpose flour until fully combined.
Pour the filling over the cooled crust and spread evenly.
Bake for another 20 minutes until the filling is set.
Let cool completely before removing from the pan and cutting into squares.