Heat a saucepan with vegan butter or oil. Add the minced onion and saute for ∼3 minutes until translucent. Add the sugar and caramelize the onions for a ∼2 minutes
Stir in the tomato purée and flour.
Add the balsamic vinegar, wine, and water. Let it simmer for about 10 minutes at medium heat until the gravy has thickened. Add more water if the sauce gets too thick