Cake: Heat oven to 350 degrees. Grease and flour 2 9-inch round baking pans. In large mixer bowl, combine dry ingredients. Add buttermilk, eggs, oil and vanilla. Beat on medium speed for 2 minutes, Remove from mixer; stir in boiling water. Pour into prepared pans.
Bake 30-35 minutes, or until wooden toothpick inserted in center comes out clean. Cool 10-12 minutes, Remove from pans to wire rack. Cool completely.
Frosting: Combine ingredients in a large bowl, mix until smooth.