Ingredients
3/4 cup butter, softened1/2 cup sugar4 large egg yolks, room temperature1-1/2 teaspoons grated lemon zest2 teaspoons vanilla extract2 cups all-purpose flour1 teaspoon baking powderDash saltFILLING:2-1/3 cups plain whole milk yogurt1-2/3 cups sour cream1/3 cup all-purpose flour2 teaspoons vanilla extract4 large egg whites, room temperature3/4 cup sugarConfectioners’ sugar, optional
Preparation
In a large bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Add egg yolks, 1 at a time, beating well after each addition. Beat in zest and vanilla. In another bowl, whisk flour, baking powder and salt; gradually beat into creamed mixture.
Divide dough in half. Shape each into a disk; wrap. Refrigerate 1 portion and freeze 1 portion for 30 minutes.
Preheat oven to 350°. On a lightly floured surface, roll refrigerated portion of dough to fit a greased 15x10x1-in. baking pan. Refrigerate while making filling.
Meanwhile, for filling, in a large bowl, combine yogurt, sour cream, flour and vanilla. With clean beaters, beat egg whites on medium speed until soft peaks form. Gradually add granulated sugar, 1 tablespoon at a time, beating on high after each addition until sugar is dissolved. Continue beating until stiff glossy peaks form. Fold into yogurt mixture. Spread evenly over crust.
Using a box grater, grate frozen dough portion over filling. Press lightly into filling. Bake until puffed and edges are light brown, 30-35 minutes. Cool completely on a wire rack. Cut into bars; if desired, sprinkle with confectioners’ sugar. Refrigerate leftovers.
