Cut tamarillos almost in half lengthways, leaving stem end intact, set aside.
Combine sugar, wine, vanilla bean and seeds and 250ml water in a saucepan, bring to the simmer over medium heat, stirring to dissolve sugar (3-5 minutes). Add tamarillos, cover with baking paper, weight with a plate, cook over low heat until tender (5-10 minutes).
Remove tamarillos from syrup, then reduce syrup over high heat to 800ml (10-15 minutes). Cool slightly, then pour over tamarillos and refrigerate until chilled (2 hours). Serve tamarillos with chocolate mousse.