Sauté the Onions: Heat olive oil and butter, then add onions, thyme, bay leaves, salt, and pepper. Sauté for about 10 minutes until softened.

Caramelize the Onions: Reduce heat to medium-low and cook for 40 minutes, stirring frequently until golden-brown.

Add Garlic and Wine: Stir in minced garlic and sherry wine, deglazing the pot. Simmer until wine reduces slightly.

Incorporate the Stock: Add beef stock and simmer for 10 minutes, allowing flavors to meld. Turn off heat and cool slightly.

Preheat and Prepare Baking Dish: Preheat oven to 350°F (175°C) and greas the baking dish.

Prepare the Bread Mixture: Tear bread into pieces and combine with whisked eggs and onion mixture. Toss gently.

Assemble in Baking Dish: Spread bread mixture evenly in the dish and pour remaining onion mixture over the top.

Bake to Perfection: Bake uncovered for about 35 minutes until heated through and top is golden.

Broil for a Cheesy Finish: Broil for 1-2 minutes adding remaining cheese until bubbly and browned.

Garnish and Serve: Cool slightly before serving, garnishing with pepper and thyme.