Cream together sugar and butter; beat in egg and vanilla. Add flour, baking powder and salt; mix thoroughly. Roll dough into two rolls. Wrap in waxed paper and freezer wrap. Freeze until ready to bake. Slice cookies 1/4-inch thick and place on cookie sheet. Bake at 350 F for 10-12 minutes or until lightly browned. Watch closely during baking. Yield: about 3 dozen cookies.