In the bowl of a food processor, add the flour, sugar and kosher salt. Pulse a few times to combine.
2 cups all purpose flour, ½ cup powdered sugar, ½ tsp. kosher salt
Pulse the mixture while gradually adding the cold butter cubes. Then pulse a few more times until all of the butter cubes have been added. The mixture will still look crumbly, and you will think, this can't be right.... this IS right!
1 cup cold salted butter cubed
Transfer the crumbly shortbread mixture to a 9×13 inch pan and firmly press with fingers into an even layer. The bottom of a 1 cup measuring cup works great too for pressing it evenly into the pan.
Bake for 15 minutes until starting to just become golden brown around the edges.
Add your preferred filling on top of the crust and bake per the instructions of your recipe.