1In 1-quart saucepan, melt sweet baking chocolate over low heat, stirring frequently. Place waxed paper on cookie sheet. Spread melted chocolate in 8-inch square on waxed paper. Refrigerate until firm, about 1 hour.
2Remove chocolate from refrigerator; let stand until room temperature. Cut with cookie cutters of desired shapes and sizes. Refrigerate until ready to place on cupcakes. Carefully peel cutouts from waxed paper, handling as little as possible. Dip half of each cutout into melted white baking chocolate; refrigerate until set.
3Heat oven to 350°F. Line 36 regular-size muffin cups with paper baking cups. In large bowl, beat all remaining ingredients except frosting with electric mixer on low speed 30 seconds, scraping bowl constantly. Beat on high speed 3 minutes, scraping bowl occasionally. Pour batter into muffin cups, filling each 1/2 full.
4Bake 20 to 25 minutes or until toothpick inserted in center comes out clean. Remove from pan to cooling rack. Cool completely, about 30 minutes. Spread with frosting. Garnish with chocolate cutouts.