Insert metal accessory rack.
Preheat oven to 350°F.
In medium mixing bowl, cream butter and granulated sugar with an electric mixer until light and fluffy.
Beat in lemon rind, egg yolk, lemon extract and vanilla.
Gradually add flour and beat until blended.
Roll 1 tablespoon of dough to form ball.
Place on ungreased cookie sheet.
Dip bottom of 2 1/2 inch round glass into sugar.
Using bottom of glass, flatten to 1/4 inch thickness.
Bake 9 to 12 minutes until cookie edges begin to brown.
Let cool on wire rack.
Sift powdered sugar over top.