Preheat oven to 350°F. Beat butter and sugar in large bowl with electric mixer on medium speed until light and fluffy. Add eggs, vanilla, cake mix, baking powder and milk. Beat 3 minutes, scraping sides of bowl occasionally. Spoon batter into 2 greased and floured 8- or 9-inch round cake pans.
Bake 30 to 33 minutes or until toothpick inserted in center comes out clean. Cool 15 minutes; invert cakes onto wire racks. Turn layers right side up and cool completely.
Spread one cake layer with icing and a layer of strawberry or raspberry preserves, if desired. Top with second cake layer. Frost top and side of cake with remaining icing. Cover the frosted sides of the cake with sprinkles, if desired.