Finely slice the onions. In a Dutch oven or heavy pot, cook the red onions with a little olive oil and pancetta over medium heat for about 15 minutes. Deglaze with 1/4 cup (about 60 ml) of white wine.

Add garlic, sugar, salt, and enough vegetable broth to cover the onions. Continue cooking for another 30 minutes. Meanwhile, toast the bread slices until golden brown.

Ladle the soup into small oven-safe bowls over the toasted bread slices. Sprinkle with Pecorino Toscano cheese and bake for 5 minutes, until a golden crust forms on top.