Chocolate Cupcakes with White Chocolate Icing

Position oven racks on upper and lower thirds of oven and preheat to 350 degrees F.

Line two 12-cup cupcake pans with baking cups. Fill each cup 3/4 full with cake batter. Bake cupcakes until tester inserted into center comes out clean, rotating baking sheets from top to bottom halfway through baking, about 18 minutes. Cool cupcakes in pan on rack. Turn cupcakes out onto racks and cool completely.

Stir white chocolate in top of double boiler over barely simmering water until smooth. Heat cream in heavy small saucepan over medium heat until small bubbles form around pan sides, about 2 minutes. Pour hot cream into chocolate; stir to blend. Transfer mixture to medium heatproof bowl or container. Cool to room temperature. Cover tightly with plastic and refrigerate until ganache is thick but not firm, stirring occasionally, about 1 hour.

Using electric stand mixer and flat beater attachment, beat butter until fluffy, about 2 minutes. Add ganache and beat on medium speed until soft peaks form, about 4 minutes.

Using an offset spatula, spread some icing over cupcakes. Spoon remaining ganache into pastry bag fitted with open star tip (#6 tip). Pipe icing onto tops of cupcakes in a large rosette design.

DO-AHEAD TIP: Cupcakes can be made 3 days ahead. Store in airtight container and refrigerate. Let stand 20 minutes at room temperature before serving.