CAKE: Preheat oven to 325 degrees. Lightly grease a 9 x 13-inch pan, set aside.
In a large bowl combine cake mix, eggs, club soda, 1 box of the pudding and oil, beat until smooth, stir in a 1/2 cup nuts. Pour into prepared pan.
Bake for 30-40 minutes. Cake is done when a toothpick comes out clean. Cool in pan on a rack. When completely cool, frost cake with icing.
FROSTING: Mix 1-1/2 cups milk, instant whipped topping, and 1 box instant pistachio pudding. Beat on low to combine and then on high for 4 minutes. Fold in 1/2 cup nuts and spread on cooled cake. Keep cake refrigerated.
Cook's Note: If desired, bake in a well greased and floured Bundt pan for 45 minutes.