45g (1 1/2oz) butter 1tbsp sunflower oil 1kg (2Ib) large onions, thinly sliced 2tsp caster sugar 30gm (1oz) plain flour 1.8 litres (3 pints) vegetable, chicken, or beef stock salt and black pepper 8 Gruyère croûtes (Slices from a baguette and toast on one side under a hot grill. Remove from the heat and turn the slices over. Grate Gruyère cheese evenly over the untoasted sides of the bread slices. Return to the girll and cook until the cheese has melted and is gently bubbling)

Cook the onions in the butter and oil for a few minutes until soft. Add the sugar and continue cooking over a low heat, stirring occasionally, for 20 minutes or until the onions are golden brown.
1- Met the butter with the oil a large saucepan, and caramelize the onions with the sugar . Sprinkle the flour into the pan and cook, stirring constantly, for 1 – 2 minutes.
2- Gradually stir in the stock and bring to a boil. Season with salt and pepper, then cover and simmer, stirring from time to time, for 35 minutes.
3-Taste the soup for season, then ladle into warmed bowls. Float a Gruère croûte in each bowl and serve at once.

Cook’s know – how
Cooking with sugar is the key to developing a rich, golden brown colour and sweet caramel flavour in onions. It is this that produces the characteristic appearance and taste of this classic soup.