Beat butter with sugar in a mixer until light and fluffy. Then sift the flour into the bowl and knead the dough.
Lay the dough on a flat surface and form a long rectangular prism with your hands.
Run the dough in a layer of sugar, wrap in cling film and put in the refrigerator for an hour.
Cut the dough into squares, put on parchment and bake for 20 minutes at 325 F.