How to cook
Cut the onions into thin round slices and saute them in butter on medium heat. While stirring, add the finely chopped leeks, the crushed garlic, broth cubes and 4 1/5 cups (1 liter) of water.
Season the soup with thyme, salt and pepper to taste. Let it boil on medium heat for about 20-25 minutes. Near the end of cooking, add the white wine. Put the soup in the oven in a suitable container, cover the top with lightly fried cubes of bread.
Add grated emmental cheese on top of the cubes and bake for about 10 minutes at 536°F (280 °C) until the top is lightly browned. Serve the soup hot.