French onion soup

French onion soup – Serves 2
To make French onion soup, you need to fry the onion until the natural sugars caramelise and the onions turn brown. This gives the soup its delicious flavour and sweet taste, and also provides colour.

25g butter or margarine
1 tablespoon oil (15g)
4 medium onions thinly sliced (450g)
1 tsp sugar
2 garlic cloves, thinly sliced
1 heaped tablespoon plain flour (30g)
600ml boiling water
1-2 beef or vegetable stock cubes
4 slices French bread (depending on size)
50g grated cheese


  1. Melt the butter with the oil in a large heavy-based pan.
  2. Add the onions and stir and fry for 10 mins until soft, then sprinkle in the sugar, add the garlic and cook for 5 minutes until caramelised. The onions change to a golden brown colour and become sweet.
  3. Stir in the flour, add the boiling water and stock cubes and stir to thicken.  Cover and simmer for 10 minutes.
  4. To serve, toast the bread under the grill, scatter on the cheese and grill until bubbling.
  5. Spoon the soup into heat-proof bowls, float 2 slices of cheesy toast on top each bowl and serve.

The science bit

When the onions are heated, the sugars turn to caramel and the onions become brown.
The caramel gives the soup its brown colour and sweet flavour.
Flour is added to the soup liquid to thicken it. The starch in the flour gelatinises, swells and thickens the liquid.
The toast turns brown when it is toasted as dextrin is formed.
The cheese melts with heat, and the protein coagulates and shrinks.

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Filed under Food GCSE Recipes, Food science

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