Preheat oven to 350 degrees and line 6 1/2 cup muffin tins with paper liners.
In a small heatproof bowl cover cranberries with boiling water and soak 5 minutes.
While cranberries are soaking, into a bowl sift together flour, cornstarch, baking powder, cinnamon, nutmeg, and a pinch salt. In another bowl with an electric mixer beat together butter and sugar until light and fluffy and beat in egg, 1 tablespoon at a time, beating well after each addition. Beat in vanilla. Stir in flour mixture and milk alternately in several batches, beginning and ending with flour and stirring until smooth after each addition.
Drain cranberries and pat dry. Chop cranberries fine and stir into batter. Divide batter among muffin tins and bake in middle of oven until a tester comes out clean, about 20 minutes.
Making frosting while cupcakes are baking:
In a bowl beat together frosting ingredients until smooth and chill.
Turn cupcakes onto a rack and cool 10 minutes. Spread cupcakes with frosting.
Recipe Courtesy of Gourmet Magazine