Grease and flour an 11-inch fluted tart pan with removable bottom or a 2-quart rectangular baking dish; set aside.
In a large bowl combine flour and granulated sugar. Cut in butter until mixture resembles coarse crumbs. Set aside 1/2 cup mixture for topping.
For batter stir baking powder, soda, nutmeg, and salt into remaining crumb mixture. Make a well in the center. In a small bowl combine egg, buttermilk, and vanilla. Add egg mixture all at once to nutmeg mixture. Stir just until moistened (batter should be lumpy). Set aside 1 cup batter.
Spread remaining batter onto bottom and 1 inch up sides of prepared pan or dish. Carefully spread the desired pie filling on top. Spoon reserved batter into small mounds on top of filling. Sprinkle with topping.
Bake in a 350 degree F oven about 45 minutes for tart pan or about 40 minutes for baking dish or until golden. (If necessary, cover edges with foil after 30 minutes to prevent overbrowning.)
Cool in pan on a wire rack for 15 minutes. If using tart pan, remove side and bottom. Drizzle with Vanilla Icing. Serve warm, or cool on wire rack. Makes 8 servings.
Stir together powdered sugar, vanilla, and enough milk to make drizzling consistency.