Heat your oven to 350°F (175°C). Lightly spray a 9x13-inch baking pan with non-stick spray. Alternatively, divide the mixture between two 8x8-inch pans.
In a medium bowl, mix the flour, sugar, and salt.
Cut the cold butter into the flour mixture until it resembles coarse crumbs. Be sure to keep the butter cold to maintain a flaky texture.
Stir in the milk until the dough comes together. If it’s too dry, add more milk, a little at a time. Press the dough firmly into the prepared pan and smooth it with your fingers or the bottom of a measuring cup.
Dock the dough gently with a fork to prevent puffing during baking. Chill the dough in the fridge for at least 15 minutes.
Bake for 15-20 minutes, or until the crust is set and begins to brown around the edges (this is called par-baking). Let the crust cool.