1Heat oven to 350°F (325°F for dark or nonstick pans). Place mini paper baking cup in each of 70 mini muffin cups. Finely chop enough candy to equal 3/4 cup (about 2 bars).
2In large bowl, beat cake mix, water, oil and egg whites with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. On low speed, beat in chopped candy just until blended. Divide batter evenly among muffin cups (two-thirds full). Refrigerate any remaining cake batter until ready to use.
3Bake 12 to 16 minutes or until toothpick inserted in center comes out clean. Cool 5 minutes; remove from pan to cooling rack. Cool completely, about 30 minutes.
4Frost cupcakes with frosting. Coarsely chop remaining candy. Place candy pieces on frosting, pressing down slightly. Store loosely covered.