Step 1

Heat a large pot like a Dutch oven over medium heat. Melt butter and add the olive oil. Add the sliced onions and season with 1/2 tsp salt.

Step 2

Cook over medium heat, stirring often, for 45-50 minutes, or until the onions start to caramelize and have a deep golden brown color. If they start to burn at any point, add a splash of water to bring the temperature down. Towards the end of cooking, increase the heat to medium-high, and start stirring contantly to prevent burning.

Step 3

When the onions are nearly done, add the garlic and fresh thyme. Cook for 1-2 minutes or until fragrant, stirring often.

Step 4

Add the flour and cook for 1 more minute, stirring vigorously.

Step 5

Gradually pour 1 cup of vegetable broth while stirring constantly. Don't forget to stir the bottom of the pot to get any browned bit off. Add the soy sauce.

Step 6

Pour the rest of the vegetable broth (5 cups) and add the bay leaves and black pepper.

Step 7

Cover with a lid and simmer on medium-low heat for 30 minutes. At the end, stir 2 tsp red wine vinegar. Taste and adjust the flavor if needed, adding more salt or black pepper to taste. You can also add more vinegar if you want more acidity.

Step 8

In the meantime, turn the broiler in the oven on. Place bread slices on a baking sheet and place the sheet in the second to top rack in the oven. Broil for 1-2 minutes per side, flipping once golden brown. When ready, take the bread out of the oven.

Step 9

Divide the soup between oven-safe bowls and top with 1-2 bread slices and shredded cheese (I usually add 1/2 cup of shredded cheese, but feel free to add less if desired). Broil for 1 minute, or until the cheese is golden brown. Take it out of the oven and serve the soup right away!