Watergate Cake

1 box white cake mix
3 egg whites
3/4 cup oil
1 1/2 cups 7-Up or club soda
1 box instant pistachio pudding
1/2 cup coconut
1/2 cup chopped black walnuts Cover Up Frosting:
2 envelopes dream whip
1 box instant pistachio pudding
1/2 cup scalded milk

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Blend cake mix, egg whites, oil, 7-Up, and pudding. Beat for 3 minutes, then fold in coconut and nuts. Pour into three 9″ layer pans. Bake 25-30 minutes in a 350 degree oven. Cool completely. To make frosting, beat all frosting ingredients with an electric mixer until thick enough to spread. Frost cake.