I've seen some cakes that people say they use a fudge filling or a truffle filling. Do you use a regular candy fudge or truffle recipe?
The truffle recipe I use is on the google doc from Macsmom. It's awesome and easy. If you go into the Cake Ideas forum and click on the forum about Gourmet Flavors, you'll find it. It's part of her signature line. I have used a lot of the recipes from it and they always come out great. Let me know if you need more direction.