Start by thinly slicing the yellow onions. In a large, heavy-bottomed pot, melt 2 tablespoons of butter and 1 tablespoon of olive oil over low heat. Add the onions, stirring to coat, and cook for about 40–45 minutes until they turn a deep, golden brown, stirring occasionally to ensure even caramelization and prevent sticking.

Once your onions are beautifully caramelized, stir in 2 cloves of minced garlic and a few sprigs of fresh thyme. Cook for an additional minute, stirring gently to release the aromatic oils.

Pour in ½ cup of white wine or sherry, scraping the bottom of the pot to lift any browned bits. Allow the alcohol to simmer for about 2-3 minutes until reduced.

Carefully pour in 6 cups of beef broth, or vegetable broth for a vegetarian option. Bring the mixture to a gentle boil, then reduce the heat to low and let it simmer uncovered for about 30 minutes, seasoning with salt and pepper.

While the soup simmers, preheat your oven to 400°F (200°C). Slice a baguette into ½-inch thick pieces and toast them in the oven for about 10 minutes until crisp and golden.

Ladle the fragrant soup into oven-safe bowls. Place a toasted baguette slice on top of each bowl, then sprinkle with shredded Gruyère cheese.

Set your oven to broil and carefully place the bowls on the top rack. Broil for about 2-5 minutes until the cheese bubbles and turns golden brown.

Allow the bowls to cool slightly before serving your French Onion Soup, pairing it with a simple green salad or additional toasted baguette slices.