Cheese Sauce (for pasta)

Melt the butter in a saucepan. Stir in the flour and cook for 2 minutes without browning. Gradually blend in the pasta water followed by the milk. Cook, stirring, until the sauce comes to the boil and thickens. Simmer for 2 minutes. Stir in 3/4 of the cheese then season well to taste with salt and pepper.