1 pound (4 sticks) butter, softened
1 1/3 cups powdered sugar
4 teaspoons finely grated lemon peel (firmly packed)
2 1/2 cups all-purpose flour*
2 cups quick or old fashioned oats (uncooked)
1/2 teaspoon baking powder
1/2 teaspoon salt
granulated or sanding sugar
Combine butter, sugar and lemon peel in a large bowl and beat with electric mixer until creamy.
In another bowl, combine flour, oats, baking powder and salt and gradually add into cream mixture; mix well.
Divide dough in half; wrap each half in plastic wrap. Chill 1 hour or until firm.
Pre-heat oven to 325°F (160°C).
Take one portion of dough from refrigerator and roll on lightly floured surface into 10-inch squares. With sharp knife, cut into squares. Transfer squares onto ungreased cookie sheets; prick each shortbread cookie with the tines of a fork. Sprinkle lightly with sanding sugar.
Bake 15 to 18 minutes or until lightly browned. Cool 1 minute on cookie sheets; remove to wire rack. Cool completely. Store in an air-tight container.