1.For pastry, in a large mixing bowl stir together the flour & salt. Using a pastry blender, cut in shortening until mixture resembles coarse crumbs. Lightly beat egg yolk in a glass measuring cup. Add enough milk to egg yolk to make ¾ cup total liquid; mix well. Stir egg yolk mixture into flour mixture; mix well. Set aside one-third of the dough.
2. On a lightly floured surface, roll remaining two-thirds of dough into an 18x12-inch rectangle. To transfer pastry, carefully wrap it around the rolling pin; unroll into a 15x10x1-inch baking pan (pastry will hang over edges of pan). Preheat oven to 375 degrees.
3. In a large bowl combine sugar and cornstarch. Stir in apricots and cherries. Spoon into the prepared crust.
4. Roll the remaining dough into a 16x11-inch rectangle; place over fruit. Bring bottom pastry up and over top pastry. Seal edges with the tines of a fork. Prick top pastry over entire surface with the tines of a fork.
5. Bake about 40 minutes or until golden brown. Cool in pan on a wire rack. Serve warm or cool (I think it tastes best after several hours or the next day). Drizzle with Vanilla Glaze. Cut into 2x3-inch bars. Makes 25 bars.
Vanilla Glaze: In a small bowl combine 1 ¼ cups sifted powdered sugar, ½ tsp. vanilla, and enough milk (5-6 teaspoons) to make of drizzling consistency).