Don't worry, this recipe isn't for the frothy, so-called "chocolate mousse" that's made from oil and seawater. This is the delicious and sweet variety of chocolate mousse that's perfect for a cake filling or any dessert. This recipe calls for Ghirardelli chocolate and it's great for chocolate wedding cakes. It's the best filling possible because it firms up when cold, due to the butter in the mixture. This helps hold the cakes together more firmly. It softens back up at room temperature, but is great cold, too!