To rate a perfect 10, this triple-decker confection would need to lighten up and lose its one-note texture. Triple chocolate mousse cake is a truly decadent dessert. Most times, though, the mousse texture is exactly the same from one layer to the next and the flavor is so overpoweringly rich it’s hard to finish more than a few forkfuls. We set out to tweak this showy confection. By finessing one layer at a time, starting with the dark chocolate base and building to the top white chocolate…