Combine cake recipe ingredients, and mix well. Spread in well greased 9x13 pan. (You can use 8-9 inch square pan if you like the cake to be thicker). Combine Topping Ingredients, and pour over cake batter. Bake at 400 degrees for 25 minutes or until cake is golden brown. Note: Even people who say they hate rhubarb like this cake-you don't have to tell them what is in it until after they eat it.