Line a 15x10x1-inch baking pan with 18-inch-wide foil, extending the foil up over the edges of the pan; set aside. For dough: In a large bowl, stir together flour and salt. Using a pastry blender, cut in shortening until mixture resembles coarse crumbs. In a glass measuring cup, beat egg yolk with a fork. Add enough milk to the egg yolk to make 3/4 cup total liquid; mix well. Stir egg yolk mixture into flour mixture; mix well. Divide dough into three equal portions; combine two of the portions into one.
On a lightly floured surface, roll the larger dough portion into a 19x13-inch rectangle; trim edges to make an 18x12-inch rectangle. Cut leaf shapes from dough trimmings; set aside. Wrap dough rectangle around the rolling pin; unroll it onto prepared baking pan (pastry will extend over ends of pan).
In a large bowl, combine sugar and cornstarch. Stir in drained apricots and cherries. Spoon onto dough rectangle in baking pan.
Roll the remaining dough portion into a 16x11-inch rectangle. Cut several small holes in center of dough rectangle; place dough over fruit filling. Bring bottom dough rectangle up and over edges of top rectangle; fold edges in toward center of pan. Seal edges with the tines of a fork. Brush undersides of leaf shapes with water; arrange atop dough as desired.
Bake about 45 minutes or until top is golden. Cool in pan on a wire rack at least 30 minutes. Use foil to lift pie from pan. Drizzle with Vanilla Glaze. Serve warm or cool completely. Cut into rectangles. Makes 24 servings.
Bake and cool as directed. Cover and let stand at room temperature for up to 24 hours; or chill for up to 3 days. Return to room temperature to serve.
In a small bowl, stir together powdered sugar, vanilla, and enough milk (2 to 3 teaspoons) so that glaze drips off a spoon.