Makes: 2 liters. Cooking time: 1 hour.
— 50 grams butter
— 75 grams sliced onions
— 30 grams flour
— 2 liters brown stock
— 50 croûtes de flûte
— 100 grams grated Parmesan and Gruyère cheese
(1) Melt the butter in a deep saucepan. Add the sliced onions and sweat, then allow them to lightly colour golden brown by removing the lid.
(2) Add the flour, cook to a second stage roux and allow to cool.
(3) Add the brown stock and allow to simmer gently for approximately 30 minutes until the onions are cooked. Season to taste.
(4) Ladle the soup into earthenware soup bowls (marmites) and layer the surface of the soup with dried toasted slices of bread (croûtes de flûte). Sprinkle with the grated cheeses and place under a salamander grill until a golden skin is formed.