Step 1Heat the oven to 350 degrees. Brush the bottom and sides of a 9-inch round baking pan with the butter. Toss together 1/3 cup sugar and the blueberries and spoon into the pan in an even layer.
Step 2Sift together the cake flour, 3/4 cup sugar and baking powder into a large bowl. Combine the egg substitute, applesauce, milk and vanilla, stirring together well. Quickly stir the wet ingredients into the dry ingredients, just until moistened. Pour the batter over the blueberries in the pan.
Step 3Bake the cake until a toothpick inserted in the center comes out clean, about 30 minutes. Cool the cake in the pan about 5 minutes, then loosen the edges with a knife. Invert the cake onto a platter, shaking the pan slightly to loosen it. Cut the cake and serve pieces warm with a dollop of low-fat sour cream or frozen yogurt, if desired.