Preheat oven to 350°F. For the Cake, beat all ingredients in large bowl with electric mixer on low speed until mixed. Beat on medium speed 2 minutes or until well blended, scraping sides of bowl occasionally. Pour batter evenly into 2 (9-inch) round cake pans sprayed with no stick cooking spray.
Bake 25 to 29 minutes or until toothpick inserted in center comes out clean. Cool in pans 10 minutes. Remove from pans; cool completely on wire racks.
For the Buttercream, beat butter and vanilla in large bowl until light and fluffy. Gradually add confectioners' sugar, beating well after each addition and scraping sides and bottom of bowl frequently. Add milk; beat until light and fluffy. If frosting is too thick to spread, gradually beat in additional milk. Fill and frost cooled cake with Buttercream.