50g butter, plus extra for greasing
50g plain flour
1 tsp mustard powder
100g grated extra-strong cheddar
Preparing the soufflé dish: Heat oven to 200C/fan 180C/gas 6 and place a baking sheet on the middle shelf. Butter a 15cm soufflé dish generously, then sprinkle in the breadcrumbs and rotate the dish to ensure the butter is evenly coated. Tip out any excess breadcrumbs.
Making a thick white sauce: In a pan, melt the butter over a medium heat; stir in the flour and mustard. Cook, stirring, for 1 min. Take off the heat and gradually stir in the milk, mixing it in thoroughly before adding more. Return to the heat and stir continuously until very thick (around 10 mins). Transfer to a bowl and allow to cool. Crack the eggs, placing the whites into a clean bowl and stirring the yolks into the sauce. Stir in cheddar and season well.
Adding the egg whites: Use a clean whisk to beat the egg whites until peaks form that just hold their shape (electric is best as it will make the job much quicker). Then take a metal spoon and gently stir the whipped whites into the white sauce in a figure of eight.
Top-hatting: Spoon the mixture into the dish. Run a cutlery knife around the edge to create a ‘top hat’ effect; this ensures the soufflé rises above the rim and doesn’t stick. Place on the baking sheet and bake for 25-30 mins until the top is golden and risen and has a slight wobble. Serve immediately.