Beat butter at medium speed with an electric mixer until creamy. Gradually add sugar, beating at medium speed until light and fluffy. Add eggs, one at a time, beating just until the yolk disappears. Add vanilla, beating just until blended.
Sift together flour, baking powder, and salt. Gradually add flour mixture to butter mixture; beat batter at low speed just until blended. Gently fold in nectarines and blueberries. Pour batter into 2 greased and floured 8-inch round cake pans.
Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool cake layers in pans on wire racks 10 minutes. Remove from pans, and let cool completely on wire racks.
Spread 1/2 cup Cream Cheese Frosting evenly on top of one cake layer; top with remaining cake layer. Spread remaining Cream Cheese Frosting over top and sides of cake. Garnish, if desired.