French Onion Soup 5 Steps
In a large pot, melt 1/4 cup of butter over medium heat. Add the onions; cook onions until softened, stirring occasionally, about 15 minutes. Season with salt and pepper and continue to cook, stirring occasionally, until onions are deep golden brown and caramelized, reducing heat slightly if onions seem to be browning too quickly, 25 to 35 minutes more. Stir in 2 cloves of minced garlic in the last 10 minutes of cooking.
Add wine and raise heat to high. Cook until almost all liquid has evaporated, 8 to 10 minutes.
Tie thyme and bay leaves into a bundle with twine. Add broth and herb bundle to pot with onions. Bring to a boil, reduce to a simmer, and cook, uncovered, until broth is thickened and flavourful, 20 to 30 minutes. Remove from heat and whisk in remaining 1 tablespoon butter. Stir in white wine vinegar. Taste and adjust seasoning.
Heat the broiler. Cut two 1/2"-inch thick baguette slices for every serving of soup. Place baguette slices on a rimmed baking sheet and toast in oven until crisp and dry but not browned, about 1 minute per side. Rub one side of each toast with the sliced garlic clove and set aside.
Place ramekins or ovensafe bowls on a rimmed baking sheet. Top each serving of soup with two garlic-rubbed toasts. Divide cheese among the servings, covering the bread and some of the soup. Carefully transfer baking sheet to oven and broil until cheese is melted and bubbling, 4 to 8 minutes.