Combine first 4 ingredients.
Sprinkle about 3/4 cup of walnut mixture in each of 4 ungreased 9-inch round cake pans, pressing lightly into pans.
Prepare cake mix according to package directions; pour batter over walnut mixture in prepared pans.
Bake at 350Â° for 15 to 20 minutes or until a wooden pick inserted in center comes out clean.
Remove layers from pans immediately, and let cool completely.
Beat whipping cream until foamy; gradually add powdered sugar, beating until stiff peaks form.
Stir in vanilla.
Place 1 layer, nut side up, on serving plate.
Spread 3/4 cup whipped cream over layer.
Repeat with remaining 3 layers, ending with whipped cream; chill.