Cut a 2-inch piece from one cake for the eraser; set aside. Trim 1/2 inch from the uncut ends of both cakes. Line up the cakes to make 1 long cake.
Using a paring knife, score 2 lines down the length of both cakes, 1 1/4 inches in from each side. With the lines as a guide, trim the cake sides at an angle, as shown.
Mix 1/2 cup vanilla frosting, the red food coloring and 3 drops yellow food coloring in a glass liquid measuring cup. Microwave the frosting about 20 seconds, stirring every 5 seconds.
Make the eraser: Put the 2-inch piece of cake on a rack set over a baking sheet. Pour the warm pink frosting evenly over the cake. Chill until set, about 20 minutes.
Microwave the chocolate chips in a resealable plastic bag (unsealed) in 5-second intervals until melted. Push the chocolate to one corner, twist the bag and secure with tape; freeze until set.
Mix the remaining 1 1/2 cups frosting and 20 drops yellow food coloring. Frost the cake with an offset spatula, following the beveled edges.
Make the tip: Cut one end of the cake into a tip, shaving it with a paring knife so the pencil looks sharpened.
Remove the chocolate cone from the bag and trim the base to make it flat. Attach the chocolate tip to the pencil with frosting; attach the eraser to the other end.
Lay the sour belts across the end of the pencil near the eraser, trimming as needed. Gently press into the frosting to secure.
Photograph by Kang Kim
Recipe courtesy Food Network Magazine