CAKE: Beat eggs until light and fluffy. Gradually add sugar, oil and vanilla. Sift together next 5 ingredients and add to first mixture. Stir in apples and walnuts. Put in greased 13 x 9 x 2-inch pan and bake in preheated 350 oven about 45 minutes. Let cool in pan on rack 10 to 15 minutes, then spread with frosting. FROSTING: Mix all ingredients together until smooth.