Place a wide pot over high heat, allow to get hot, then add the butter, onions, and thyme and sauté for 5 minutes until the mixture turns golden.
Reduce the heat to medium-low and continue cooking for 15 minutes until the onions soften.
Add the cognac and cook for 2 minutes.
Add a spice bag filled with the cloves, bay leaves, and garlic.
Add the beef bouillon jelly and water. Season with salt and pepper and mix. Cover the pot with a lid and simmer for 30 minutes, stirring every so often.
When the soup is ready, transfer to a small clay pot or to individual ramekins. Top with baguette slices, sprinkle with grated cheese and grill, until the bread is toasted and the cheese turns golden.
Sprinkle with parsley and serve.