My husband loves to eat tiramisu so I asked him how it smells to him. He said, 'Coffee because it has espresso in it; a little Cheesy; a little Brandy smell.'
(I hate it myself, so I had to ask him.)
So if you do layers to look like tiramisu, you could use a coffee scent in the brown layer. I've never been interested in a brandy scented FO, but I'll bet there must be some available somewhere (I think I've seen something along those lines in the past), but I would guess it may discolor so depending on how dark, that could be the beige colored layer (maybe the lady-fingers). Then the white part would have to be the cheese scent, although I don't know that I've ever actually seen any FO described as having a scent like mascarpone. I wouldn't like it myself as it's a cheese I really don't like.
Anyway, that's my 2 cents.
