Preheat the oven to 200C/400F/Gas 6.
Lightly grease six ramekins and coat the insides with the dried breadcrumbs.
Melt the butter in a saucepan and stir in the flour. Cook for 2 minutes.
Off the heat, stir in the milk to get a thick, smooth sauce. Put back on the heat and bring to the boil, stirring all the time. Simmer gently for 10 minutes and then remove from the heat.
Beat in the egg yolks, cheese, mustard and the cayenne pepper and season well.
Whisk the egg whites until they are at the soft peak stage and fold into the cheese mixture with a large metal spoon.
Divide the mixture evenly between the six ramekins and place them on a baking sheet. Bake for 15 minutes until well risen and golden. Serve at once.