Preheat oven to 350°.
To prepare cupcakes, place the first 4 ingredients in a large bowl; beat with a mixer at medium speed until well blended (about 2 minutes).
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 5 ingredients (through 1/4 teaspoon salt), stirring well with a whisk. Stir flour mixture into sugar mixture alternately with buttermilk, beginning and ending with flour mixture; mix after each addition just until blended.
Place 16 paper muffin cup liners in muffin cups; spoon about 2 1/2 tablespoons batter into each cup. Bake at 350° for 18 minutes or until a wooden pick inserted in center of a cupcake comes out with moist crumbs attached (do not overbake). Remove cupcakes from pans; cool on a wire rack.
To prepare frosting, combine powdered sugar and remaining ingredients in a medium bowl. Beat with a mixer at medium speed until combined. Increase speed to medium-high, and beat until smooth. Spread about 1 tablespoon frosting on top of each cupcake.