Preheat the oven to Gas5/375degF/190degC.

Melt the butter in a heavy-based saucepan, add the cornflour and cook through. Slowly add the milk to form a thick sauce.

Stir in the Cheddar cheese, Parmesan and powdered mustard. Stirring continuously allow the sauce to become a smooth consistency.

Grease a 2 pint souffl, dish with the butter.

In a clean bowl, whisk the egg whites until they are stiff and can form soft peaks.

Add the egg yolks to the cheese sauce, season generously and mix well.

Very carefully fold the egg whites into the sauce and then pour into the buttered souffl, dish.

Cook for 35-40 minutes until souffl, is risen and golden.