I don't have a CLUE what a *Tiramisu* is - but if it's cooked in any way, the actual alcohol burns off, leaving the taste behind.
Personally, I don't think what you did was a slip/relapse.
Now, if you'd known beforehand that it possibly contained alcohol and took the entire thing to the closet to scarf it down - that'd be another thing!
Listen to your sponsor. You HAVE EARNED every second of your 10+ months sobriety!