Make guideline pattern for triangles. Use pencil and ruler to mark parallel lines, 1 1/4 in. apart, on tracing paper. Use tape to attach pattern to cake board. Cover with parchment paper.
Make candy triangles.Melt light cocoa Candy Melts candy according to package directions. Use melted candy in finely-cut parchment bag to pipe sotas in a triangle shape, 1 1/4 in. wide x 1 in. high. Overpipe bottom 1 in. to reinforce for insertion in cake. Chill until firm, about 10 to 15 minutes. Make 100 to 110 triangles; make extras to allow for breakage.
Make cake. Prepare batter following recipe directions. Bake and cool cake.
Prepare buttercream icing following recipe directions. Stack and fill for a 2-layer cake, 5 in. high. Use spatula and icing to ice cake smooth.
Insert triangles. Use toothpick and ruler to lightly mark 1 1/4 in. high sections starting from bottom of cake. Insert triangles around cake following markings, points out and angled down. For cake top, insert triangles in a circle, 3/4 in. from edge and angled out. Insert a second circle of triangles, 1 in. from the first.