Heat olive oil and butter in a large saucepan. Add the onions and sauté over medium heat, stirring occasionally for about 30 minutes, until the onions are soft and golden brown. Then add the garlic and cook for a further 2 minutes. Pour in dry white wine, bring to boil and cook until the volume is reduced by 2 times.
Add stock to the onions. Season the soup with sugar, salt, pepper, bay leaves, thyme, and brandy or sherry. Cover the soup, bring to boil and simmer for 30 minutes. Remove bay leaves and thyme from soup before serving.
Heat the oven to 200°C. Grate gruyère over the baguette slices. Bake in the oven for 3-4 minutes. Pour the soup into tureens bowls or cups, top each bowl with a baked cheese crouton, and put in the oven for 4 minutes. Sprinkle the soup with parsley and serve.
My tips and tricks
In the mood for some experiments? Try making this soup with different types of onions, for example, white, red, leeks, and shallots.
Maria Kalenska Gastronomy Blog | https://www.myodesacuisine.com/recipes/french-onion-soup/