In a large Dutch oven, heat 2 tablespoons of olive oil and 2 tablespoons of butter over medium-high heat. Add 4 sliced onions, along with 2 sprigs of fresh thyme and 2 bay leaves. Season, sauté for about 10 minutes.

Reduce the heat to low and cook the onions for about 40 minutes, stirring occasionally. Add 2 minced garlic cloves in the last minute.

Pour in ½ cup of sherry wine, scraping up browned bits from the bottom. Add 2 cups of beef stock and simmer for about 10 minutes.

Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish.

Tear the French bread into bite-sized pieces and place in a large bowl. Whisk together 2 eggs and pour over the bread, then add 4 ounces of shredded Gruyère cheese.

Pour the caramelized onion mixture over the bread and egg mixture, stirring gently. Transfer to the baking dish.

Bake uncovered for 35 minutes until the top is golden and crispy.

Sprinkle remaining Gruyère cheese over the stuffing and broil for 1-2 minutes until golden brown.

Remove from the oven, let sit for a few minutes, and serve.