Cheese Onion Soup - cooking recipe

Ingredients

1 onion, chopped
4 ounces cheddar cheese
1/2 tablespoon mustard
550 ml milk
1 tablespoon plain flour
butter

Preparation

Cook the onion in a pan with a small bit of butter until soft. Stir in the flour to create almost a roux for a minute or so.
Stir in the milk, a little at a time, and then bring up to boiling point. Add the remaining ingredients and wait until the cheese has hit melting point. Taste and season accordingly, serve warm with bread.
(I only need to add pepper).