Combine all ingredients for cupcake batter in an electric mixer fitted with a paddle attachment and run until smooth.
Line one large or two regular muffin pans with cupcake liners and divide batter among 18 cups, about 2/3 full.
Bake cupcakes for 25-27 minutes or until a toothpick inserted can be removed without wet batter.
Allow cupcakes to cool completely on a wire rack.
When cupcakes are cool, mix together frosting ingredients in an electric mixer fitted with a whip attachment, mixing until smooth and creamy.
Place icing in a piping bag and top cupcakes. You should have enough to pipe the cupcakes fairly tall. If you just want a thin spread of icing, cut the frosting amounts in half or so.
Sprinkle with jimmies and insert a paper straw cut in half, if desired for appearance.