Preheat oven to 350° F and grease a 9x13-inch baking pan.
To prepare apple dumpling dough: Sift together flour, baking powder and salt. Cut in shortening until the mixture resembles coarse crumbs. Stir in milk; mix until soft dough is formed. Knead 4 strokes, roll to 1/8-inch thickness. Cut into 6 squares.
To prepare apples: Core and peel apples, placing one on each square. Combine sugar and cinnamon, sprinkle into center of each apple. Divide the Tbsp. of butter or margarine into 6 bits (1/2 tsp. each). Add 1/2 teaspoon butter or margarine into center of each apple. Moisten edges of dough with milk; press corners up over apples and brush with milk to seal.
Place into baking pan and bake at 350° F for 30 minutes or until dough is golden brown on top.
To prepare sauce: Heat water, vinegar and butter or margarine in a small saucepan. In a separate bowl, combine corn starch, sugar, nutmeg and cinnamon. Stir dry ingredients into saucepan; simmer on low heat, stirring constantly until it begins to thicken, about 2 minutes.
Pour sauce over hot apple dumplings when they come out of the oven. Makes 6 whole apple dumplings.