Preheat oven to 350º F and grease a 9 x 13 inch baking pan with cooking spray
In a large mixing bowl combine the flour, powdered sugar and salt. Cut in the cold butter until a fine sand like mixture is formed.
Press into the prepared baking dish
Bake the crust for 15 minutes.
While the crust is baking, in a clean mixing bowl, whisk together the eggs, sugar, lemon juice, lemon zest and baking powder until well combined and fluffy. This will take about 2 minutes and can be done by hand or with an electric mixer.
Remove the crust from the oven and evenly pour the lemon custard over the top of the crust. Bake for an additional 25 minutes until the center is set.
Remove from the oven and allow to cool for at least an hour before slicing. Dust with additional powdered sugar.