1. Keep the brown stock ready.
2. Peel and finely slice the onion.
3. Slice the baguette into long flutes (allow two per portion) and place on a baking tray.
4. Grate the cheese.
5. Wash the sprigs of thyme and allow to dry.
6. Weigh all ingredients.
7. Put oil and butter into a large, heavy-bottomed saucepan.
8. Add the onions, stir well, cover with a lid and sweat gently for about 10 minutes and continue to cook until the onions become soft and dark brown in color.
9. Turn up the heat and slowly add the stock.
10. Bring to the boil.
11. Turn down the heat again and gently simmer for 15-20 minutes.
12. Pre-heat the grill to hot and toast the baguette flutes on one side.
13. Turn over and cover the flute with the grated cheese. Return to the grill and toast until the cheese melts and turns a golden color.
14. Remove from the grill, allow to cool slightly and cut into bite-size pieces.
15. Ladle the French onion soup into warmed soup bowls.
16. Place two toasted flutes into each bowl.
17. Garnish the French onion soup with sprigs of thyme and serve.