In bowl, stir together flour, sweetener, baking powder and salt; set aside. In mixing bowl, beat butter, eggs and vanilla for 1 minute. Add apple sauce, beat just until blended. Fold in flour mixture just until moistened. Using 1/3 cup of the batter, drop by spoonfuls into greased 8-inch square cake pan. Fold cocoa powder into remaining batter just until combined. Gently spoon batter into pan covering white batter and smoothing surface. bake in 350F 180C oven for 15 minutes or until tester inserted in centre comes out clean. Transfer to rack; let cool. Per serving: about 65 calories, 2 g Protein, 4 g fat, 7 g carbohydrate