How to Make It
Beat butter at medium speed with an electric mixer until fluffy; gradually add sugars, beating well. Add eggs, one at a time, beating after each addition.
Combine flour, baking powder, and salt; add to butter mixture alternately with milk, beginning and ending with flour mixture. Beat at low speed after each addition until mixture is blended. Stir in vanilla.
Divide dough into 4 equal portions; wrap each portion in plastic wrap to prevent drying out. Chill. Proceed with cookie instructions of choice.
Shape the dough into 1-inch balls, and place on lightly greased cookie sheets. Dip a flat-bottomed glass into sugar, and flatten balls to 1/4-inch thickness. Bake at 350° for 10 minutes or until lightly browned. Remove to wire racks to cool.