Steps to Savory Goodness:

1. Pour the onions into your slow cooker.
2. Drizzle in butter, olive oil, and season with salt and pepper.
3. Set to low and let it work its magic for 10-12 hours till the onions are golden.
4. Stir in the beef stock, balsamic vinegar, and thyme leaves.
5. Cook covered on low for another 6-8 hours. Season as needed, and feel free to add the brandy.
6. Get your oven ready at 350°F (180°C).
7. Spoon the soup into oven-proof bowls and place them on a baking sheet.
8. Crown each bowl with toasted bread and a sprinkle of Gruyere cheese.
9. Bake for 20-30 minutes till cheese melts. For an extra golden touch, broil for 2-3 minutes.
10. Once cooled a tad, dive into your comforting bowl of French Onion Soup! The beautiful union of caramelized onions, aromatic broth, and rich cheese guarantees a meal that hugs your soul and pleases your palate. Enjoy!