I made this Homemade Treasure Chest Birthday Cake for my grandmother’s 80th birthday party (Pirate theme: Arg Matey! Faye is Eighty!). I made 3 (or 4?) 9×12 cakes from marble cake mix (2 boxes) and froze them until it was time to assemble. The freezing helped with carving the barrel shape of the lid. I used quite a bit of frosting to get the layers to stay together (and some of the loose cutting were piled up and frosted thickly to keep them together cohesively.
I carved out the bottom of the chest to fill with candies and the top was mounted on a cake board cut to fit. I decided just to set the lid on the bottom at a bit of an angle rather than trying for a hinged lid effect (based on other comments from people’s treasure chest cakes on this site, the angled lid was usually the most complicated part). There were dowels placed under the lid section to help take the weight but it was a really hot day and the top did eventually go for a bit of a slide off the back. It was still delicious though!
The frosting is a thick chocolate faux buttercream (basic recipe from the bag of confectioners sugar) with wood grain added by carving with a fork. The details (straps, hardware) were cut from fondant and painted with black gel food colouring. The board has graham crumbs and the treasure is the standard mix of gold chocolate coins, ring pops, candy necklaces, etc. that I picked up in the bulk section at the grocery store.