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["Heat the oven to 395F/200C.", "Melt the butter in a large saucepan.", "Add the chopped leeks and cook gently until the leeks are soft but not brown.", "Stir in the flour and mustard.", "Add the milk a little at a time stirring thoroughly to create a thick, glossy sauce.", "Season with salt and a little pepper.", "Add the egg yolks and beat well with a wooden spoon until completely incorporated.", "Finally add the cheese and stir until all the cheese is melted.", "In a clean bowl beat the egg whites with an electric whisk until stiff and firmly set (about 5 minutes).", "Using a metal spoon, stir 2 tbsp of the egg white into the souffle base to loosen the mix.", "Carefully fold in remaining egg whites in two parts.", "Be very gentle and try to retain as much volume as possible.", "Lightly grease 6 individual ramekin dishes with a little butter.", "Gently spoon the mixture into the dishes filling to within 1/2""of the top.", "Place the ramekins onto a baking sheet and cook in the preheated oven for 15 minutes or until the souffles are golden and risen.", "Serve immediately with a green salad and crusty bread.", "Be quick though, the souffle will sink in a few minutes."]
