In large bowl on low speed of mixer, cream shortening and the sugar til fluffy, about 2 to 3 minutes. Add egg yolks. Add dry ingredients in two parts, alternating with the milk. In another bowl on high speed of mixer, beat egg whites til stiff peaks form. Gently fold egg whites into the batter. Batter will be thick and dough like.
Meanwhile, make the topping. In small bowl, mix together flour, brown sugar, and baking powder. Using a pastry blender, cut in butter til mixture resembles coarse crumbs