A very easy way to make white sauce. You can mix in 150g grated or cubed cheese at the end and let this melt in if that's your thing.
25g butter, chopped into small cubes
25ml olive oil
75g plain flour
salt and pepper to taste
Put all the ingredients in a saucepan over a moderate heat on the stove and whisk until piping hot and thick. Beating the mixture from the start will mean that by the time it boils it will be smooth and evenly cooked.
Use as a base for Dan Lepard's spinach and rosemary macaroni cheese.