Make truffles. In advance, use 18 oz. of dark cocoa Candy Melts candy to make 24 to 28 truffles, approx. 1 1/8 in. dia. Melt 6 oz. of Candy Melts candy according to package directions. Dip truffles in melted candy, set on parchment-covered cake board, and immediately sprinkle with ground nuts. Chill until set, about 15 to 20 minutes.
Make cake. Bake and cool two-layer 8 in. cake according to recipe directions. Fill and layer on cake board. Make chocolate buttercream icing. Use angled spatula to ice smooth with icing.
Decorate cake. Melt one bag of Candy Melts candy according to package directions. Use melted candy in cut decorating bag to cover top of cake and pipe drips down side. Arrange truffles on top of cake. Chill until set, about 15 minutes.