Key Lime Cupcakes:
3 cups all-purpose flour
1 tablespoon baking powder
1/2 teaspoon salt
2 sticks (1/2 pound) unsalted butter
2 cups granulated sugar
2 tablespoons key lime zest
1/2 cup milk
Vanilla Buttercream Frosting:
1 teaspoon vanilla extract
4 Cups sifted confectioners' sugar
2 tablespoons Milk
For the cupcakes: Preheat the oven to 300 degrees F. Line cupcake or muffin pans with 24 cupcake liners.
Sift the flour, baking powder and salt and set aside in a bowl.
In the bowl of electric stand mixer with a paddle attachment, cream the butter and granulated sugar together for about 2 minutes. Then scrape down the bowl and add the eggs one at a time. After adding all the eggs, scrape down bowl and add the milk and dry ingredients. Mix on low until well incorporated. Scrape down the bowl again and hike up from low speed to medium speed for about 20 seconds, and then scrape down the bowl for the last time.
Fill the cupcake liners three-quarters full with batter. Bake for 20 to 22 minutes, rotating the cupcakes after 12 minutes, and bake until the cupcakes are baked through. Cool the cupcakes completely.
1- In large bowl, beat shortening and butter with electric mixer until light and fluffy. Beat in vanilla.
2- Gradually add sugar, one cup at a time, beating well on medium speed. Scrape sides and bottom of bowl often. When all sugar has been mixed in, icing will appear dry.
3- Gradually add milk; beat at medium speed until light and fluffy.
4- For thin (spreading) consistency icing, add 2 tablespoons light corn syrup, water or milk.