Annie Bell's Cheese Souffle Mash

1. Peel and cut up the potatoes, then simmer in a pan of boiling salted water until tender.
2. Preheat the oven to 220C/200C fan/ 425F/gas 7. Use a little butter to grease a 30cm oval gratin or ovenproof dish or a soufflé dish of a similar size and dust it with a couple of tablespoons of the grated parmesan.
3. Weigh out 50g butter and cut into cubes. Cut the cheddar into 1cm dice.
4. Drain the potatoes in a colander, then pass through a mouli-légumes or sieve into a bowl. Add the 50g diced butter to the warm potatoes and once it has melted stir in the milk, some seasoning and a grating of nutmeg: you should have a sloppy mash.
5. Using an electric whisk, whip the egg whites in a medium-size bowl until stiff, then fold into the mash in two goes. Next, fold in the diced cheese. Check the seasoning.
6. Transfer the mixture into the prepared dish, scatter over the rest of the parmesan and bake for 20-25 minutes until puffy and golden. Serve immediately either to accompany a roast or on its own with a green salad.