HEAT oven to 350°F.
BEAT first 6 ingredients in large bowl with mixer on low speed just until moistened, stopping frequently to scrape side of bowl. Beat on medium speed 2 min. Stir in chopped chocolate and 2 Tbsp. crushed candy. Pour into 2 lightly greased 9-inch round pans.
BAKE 35 to 40 min. or until toothpick inserted in centers comes out clean. Cool 10 min. Loosen cakes from sides of pans; invert onto wire racks. Carefully remove pans. Cool cakes completely.
FILL and frost cake with COOL WHIP. Sprinkle with remaining crushed candy just before serving. Keep refrigerated.