This recipe is from http://www.kingarthurflour.com/
3/4 cup unsalted butter, at room temperature
3/4 cup sugar
1 tablespoon orange, lemon, or lime zest
1 1/2 cups King Arthur Unbleached All-Purpose Flour
1/2 teaspoon salt
2 teaspoons baking powder
2 tablespoons fresh orange, lemon, or lime juice
1/4 cup milk
3 large eggs
1/3 cup unsalted butter
1/3 cup shortening (or use all butter)
1/8 teaspoon salt
4 to 5 cups glazing or confectioners’ sugar
2 teaspoons vanilla extract, or the flavor of your choice
1/4 to 1/3 cup milk or cream
food color, if desired
Preheat the oven to 375°F. Lightly grease a mini-cheesecake pan or standard muffin tin.
To make the cakes: Cream the butter, sugar, and zest until pale and fluffy, scraping the sides and bottom of the bowl occasionally. Whisk together the flour, salt, and baking powder, and beat into the butter mixture until a paste forms. Stir in the citrus juice and milk, scraping the sides and bottom of the mixing bowl. Add the eggs one at a time, scraping the bowl between additions, and beat until the batter is light and fluffy.
Spoon the mixture into the wells of the prepared pan and bake for 18 minutes, until the cakes are golden brown, the tops spring back when lightly touched, and a cake tester inserted in the center comes out clean. Remove from the oven and cool on a rack for 5 minutes. Remove the cakes from the pan and return to the rack to cool completely.
To make the frosting: Beat together the butter, shortening, and salt till fluffy. Add about half the sugar, and beat slowly till well blended. Add the vanilla and half the milk, and beat until fluffy. Continue mixing in sugar and milk alternately until they’re completely incorporated, then beat until the frosting is light and fluffy. Color the frosting as desired, then spread on the cakes.