For the soup, peel 500 g onions, halve them and cut or slice them into thin strips. Wash the thyme, shake dry and remove the leaves.
Heat 3 tablespoons of oil in a large pot, fry the onions in it over a low heat for about 10 minutes while stirring until transparent, do not brown. Add 1 teaspoon sugar and continue steaming for 3-5 minutes until the onions begin to caramelize.
Add wine and 3⁄4 l water, bring to the boil. Stir in stock, add bay leaf and thyme. Cover and simmer for about 15 minutes.
For the meatballs, finely dice 1 small onion. Peel garlic and chop finely. Grate the parmesan. Knead the minced meat, diced onion, garlic, parmesan, breadcrumbs, tomato paste, a little salt and pepper well.
Form 16 miniature mince balls from the mince mixture. Heat 2 tablespoons of oil in a frying pan. Fry the meatballs in it for about 4 minutes, then take them out.
Line a baking tray with baking paper. Finely dice the mozzarella, grate the Gruyère. Mix both cheeses. Preheat the oven grill. Put baguette slices on the baking tray, place 2 meatballs on each. Sprinkle with the cheese mixture.
Gratinate under the grill for 4-5 minutes. Season soup with salt and pepper. Arrange in deep bowls with 2 cheese baguettes each.