Cream 1/2 cup brown sugar and margarine at medium speed of an electric mixer until light and fluffy (about 5 minutes). Add egg, and beat well. Add egg whites, and beat well. Combine yogurt and applesauce. Combine flour and next 3 ingredients; add to creamed mixture alternately with yogurt mixture, beginning and ending with flour mixture. Mix well after each addition. Reserve 1 cup batter, and set aside. Combine cream cheese and milk, stirring with a wire whisk until smooth. Pour remaining batter into a 9-inch square baking pan coated with baking spray. Spoon cream cheese mixture over batter. Top with 1 cup chopped apple. Pour 1 cup reserved batter over apple; top with remaining 1/2 cup apple. Sprinkle with 1/4 cup brown sugar. Bake at 350° for 55 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack. Yield: 16 servings (serving size: 1 [2-1/4] -inch square). Calories 146 (29% from fat), protein 3.3g, Fat 4.7g (Sat 1.5g, Mono 1.7g, Poly 1g), carb 23.1g, Fiber 0.7g, Chol 18mg t iron 1mg, sodium 165mg, calcium 50mg dess101