Beat Egg Whites Until Peaks Form. Add Sugar Gradually. Add Yolks; Beat 3 Minutes. Combine Flour And Baking Powder; Add To Egg Mixture Alternately With Milk. Pour Into Well Greased 9 X 13-Inch Pan. Bake At 350 Degrees F. For 30 To 40 Minutes. Pour Sauce Ingredients Into Blender; Blend. Punch Holes In Cake With Toothpick While Yet Warm; Pour Sauce Over Cake. Allow Cake To Cool In Refrigerator Before Frosting. To Make Frosting: Mix All Ingredients In The Top Of Double Boiler. Cook For 7 To 10 Minutes While Beating Constantly. Frost Cake. Keep Refrigerated.