Baked French Onion Soup Recipe

Make Beef Stock

In a large pot, add the beef bones, water, whole onion, whole carrot, whole celery stalk, bay leaves, black peppercorns, and salt. Bring to a boil over medium-high heat.

Reduce the heat to low and let it simmer for about 4-6 hours, skimming off any foam that rises to the top. The stock is done when it has a rich flavor and color.

Once finished, strain the stock through a fine-mesh sieve into a clean pot and discard the solids. Set aside.

Caramelize Onions

In a large saucepan, heat the butter and olive oil over medium heat. Add the sliced sweet onions and a pinch of salt. Cook, stirring frequently, until the onions are caramelized and golden brown, about 30-40 minutes.

Add minced garlic and thyme leaves to the onions, cooking for an additional 2 minutes.

Pour in the prepared beef stock and bring to a simmer. Season with salt and black pepper to taste. Let it simmer for another 20 minutes to combine the flavors.

Prepare for Baking

Preheat the oven to 400°F (200°C). Slice the French baguette into thick slices.

Ladle the onion soup into oven-safe bowls. Place a slice of baguette on top of each bowl and sprinkle with Gruyere and Parmesan cheese.

Place the bowls on a baking sheet and bake in the preheated oven for 15-20 minutes, or until the cheese is bubbly and golden.

Remove from the oven, garnish with chopped chives, and serve hot.