Preheat the oven to 325 degrees F (165 degrees C). Line a 9-inch square pan with foil, leaving an overhang on all sides.

Mix butter and sugar together with a spoon until texture is sandy. Slowly mix in flour. Knead dough a few times until crumbly, not smooth. Pat dough over the bottom of the prepared pan. Prick all over with a fork.

Bake in the preheated oven until set, about 45 minutes. Score with a knife while still warm. Lift out foil and let cookies cool on a baking rack. Break apart on cut lines when completely cooled.