- 3–4 thin leeks (weighing 350g before you trim them)
- 40g (1½oz) butter
- 40g(1½oz) flour
- 275ml (10fl oz) milk
- 4 free-range egg yolks
- salt and freshly ground black pepper
- a pinch of freshly grated nutmeg
- 6 free-range egg whites
Melt the butter in a medium-sized saucepan and add the flour; cook for a few seconds then pour in the milk. Stir the mixture over a high heat until it first goes lumpy then smooth and very thick.
Transfer the sauce to a large bowl – this cools it slightly ready for adding the yolks and is more convenient later when you want to fold in the egg whites. Beat in the egg yolks one by one then gently stir in the leeks. Season the mixture with salt, pepper and nutmeg – be fairly generous because the egg whites will dilute the flavour. You can now leave this mixture until just before you want to cook the soufflé. I have kept it for several hours in the fridge and it has been perfect.
Before cooking, whisk the egg whites until they’re thick and standing in soft peaks, but don’t let them get hard and dry.Stir a generous heaped tablespoon of egg white into the leek sauce mixture to loosen it, then tip all of the egg white on top of it and gently fold it in with a metal spoon. When it has pretty well all been incorporated, pour the mixture gently into your prepared dish – it needs to come up almost to the rim, but no higher; if it is lower it will still taste good even though it won’t look so impressively high and puffy, but if it is piled above the rim it will overflow.
To cook the soufflé, place on a baking sheet on the middle shelf of a preheated oven, 190oC, 375oF, Gas Mark 5, and bake for 30–35 minutes or until it looks firm when you move the dish slightly and a skewer pushed down gently into the soufflé comes out clean. If it’s done before you’re quite ready, turn off the oven and the soufflé will keep for 4–5 minutes longer although it won’t be quite so puffy.