Italian Cream-Filled Cake

Directions

1. 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.
2. Divide dough in half. Shape each into a disk; wrap. Refrigerate 1 portion and freeze 1 portion for 30 minutes.
3. 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.
4. 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.
5. 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.