Combine strawberries and the 2 tablespoons sugar. Cover and let stand in the refrigerator for at least 1 hour or up to 3 hours.
In a mixing bowl stir together flour, the 1 tablespoon sugar, baking powder, and baking soda. Cut in margarine until mixture resembles coarse crumbs. Combine egg and buttermilk. Add to flour mixture all at once, stirring until combined.
Spray an 8-inch round baking pan with nonstick spray coating. With lightly floured hands, pat dough into pan. Bake in a 450 degree F oven about 10 minutes or until golden. Cool in pan 10 minutes. Remove from pan and cool completely, or serve shortcake warm.
Meanwhile, prepare whipped dessert topping mix according to package directions using the skim milk.
Split shortcake into 2 layers. Place the bottom layer on a serving plate. Top with some of the berries, then add the second layer of shortcake. Spoon dessert topping and the remaining strawberries on top of cake. Makes 8 servings.