Put the potatoes in a pan of cold salted water and cook for 20 minutes, or until tender. Drain, mash in the pan over a gentle heat for 2 minutes to dry a little. Put in a bowl and cool for 10 minutes.

Preheat the oven to 200°C/180°C fan oven/Gas Mark 6. Butter six 250 ml (9 fl oz) ramekins, sprinkle each with 1 tablespoon of the parmesan and put them on a baking sheet.

Add the cheese sauce, mustard and egg yolks to the potato, season well with salt and pepper and beat together.

Whisk the egg whites in a clean, grease-free bowl until stiff peaks form, then fold them into the mashed potato. Spoon into the prepared ramekins and bake for 30 minutes until well risen. Serve immediately.