I've had a lot of success with the recipes in Wayne Gisslen's PROFESSIONAL BAKING, but I punched the flavors up a bit. The joconde is not very tasty on its own, so try adding rum and coffee to to syrup, and brush it on to soak the sponge well. Also, adding espresso powder to the buttercream, and some to the ganache, will harmonize the overall flavor. Take care not to make the layers too thick (1/4" is fine). As for the topping, some recipes advocate a ganache-style icing. Gisslen has a one for Opera Glaze, combining couverture and peanut oil that works pretty well. The idea is to have a smooth, almost shiny surface that can be cut easily with a warm knife. Opera takes a lot of work, but it's fun and can be well worth the effort. Good luck.