Preheat oven 375. Line cookie sheet with parchment paper or spray cookie sheet.
Combine butter and sugar in large bowl, beat @ med till fluffy. Beat in egg yolks and lemon peel.
Combine flour,cornstarch,baking powder and salt in med bowl.Gradually add flour to butter mixture, Beat @ low just til crumbly. Stir in blueberries.
Using your hands form dough into a ball. On a sheet of wax paper knead dough til it holds together.Divide the dough in 1/2.
Form each 1/2 into a disc shape, cut into 1/4ths. Roll each quarter into a disc, again cut into 1/4ths.
Each 1/2 will now give you 16 pieces.32 cookies total.
Roll each piece into a ball and place 2" apart on cookie sheet
Flatten each ball with a glass dipped in sugar.
Bake @ 375 for 12-14 min or until cookies are lightly browned around the edge