Place the onions in the slow cooker.
Add the melted butter, olive oil, salt, and pepper.
Cover and cook on low for 10-12 hours until the onions are golden brown and tender.
Stir in the beef stock, balsamic vinegar, and fresh thyme.
Continue to cook on low for another 6-8 hours. Season with additional salt and pepper as needed, and optionally add the brandy.
Preheat the oven to 350°F (180°C).
Ladle the soup into oven-safe bowls arranged on a baking tray.
Top each with a slice of toasted bread and a generous amount of Gruyère cheese.
Bake for 20-30 minutes until the cheese melts, then broil for 2-3 minutes until the cheese is bubbly and golden brown.
Carefully remove from the oven, let it cool slightly, and serve.
This Slow Cooker French Onion Soup is a delectable, comforting dish that epitomizes the perfect blend of caramelized onions, savory broth, and melted cheese. It’s a delightful and satisfying meal that will surely warm your soul and appease your cravings for a cozy, comforting dish
