How To Make Your Own Geode Cupcakes and Cookies For Your Daughter's Birthday Party. SUPPLIES & TOOLS: Preferred cake mix Cupcake pans & liners Sugar cookies Royal icing for cookies Buttercream icing for cupcakes Rock candies Basic baking tools DIRECTIONS: After cupcakes are cooled, apply buttercream icing. Follow the same directions for the cookies, using royal icing instead of buttercream. Using two complementary colors of rock candy, arrange them to form a geode shape on top of the icing Pro Tip: You can use a little food coloring diluted with water and a paintbrush to fill in gaps and smooth out color transitions.