1 1/2 sticks of butter, softened
1/2 cup of confectioners' sugar
In a large bowl, cream together the butter and the confectioners' sugar.
Mix the flour and the salt together in another bowl, then add this to the butter mixture.
Add in the vanilla and the lemon zest and mix well.
Gather up the dough into a ball and wrap it in wax paper. Put the wrapped ball in the refrigerator for four hours. (Or one hour, if you're really impatient like me.)
Take the dough out of the refrigerator and let it sit while the oven is preheating. (Turn the oven on to 325° F.)
Press the dough into an 8-inch-square pan. Sprinkle it with the sugar.
Bake about 20 minutes, just until the edges of the dough start to turn a light brown.
Remove the pan from the oven and let it cool.
Cut into 2 x 2-inch squares.