Finely chop parsley. Zest lemon and mix with parsley; set aside in a small bowl. Peel and finely chop garlic. Grate Gruyère cheese and set aside. Peel and thinly slice onions.
Heat ghee in a large pot over medium heat. Add thyme, sliced onions, garlic, and bay leaf. Stirring constantly, cook over high heat for approx. 5 – 10 min., or until the onions become transparent. Reduce heat to medium and cook for approx. 10 min. more.
Add brown sugar, salt, and pepper to the pot. Pour in the vegetable stock and wine and cook over medium heat for approx. 30 min.
Pre-heat oven to 200°C/390°F. Pour the soup into an ovenproof pot if needed, preferably cast iron. Sprinkle with grated Gruyère cheese and bake in the oven for approx. 10 min., or until the cheese is melted and starting to bubble and brown.
Slice baguette. Melt butter over medium heat in a frying pan. Toast both sides of the baguette slices in the pan until crispy. Season with salt.
Remove the soup from the oven and top with parsley-lemon zest mixture. Serve with toasted baguette. Enjoy!