This recipe is adapted from Delia's Happy Christmas
50g trimmed spring onion, finely chopped (including the green part)
110g boiled potatoes, grated
30g grated Cheddar (plus 1 dessertspoon for later)
30g grated Parmesan (plus 1 dessertspoon for later)
4 tablespoons soured cream (80g)
4 tablespoons Greek thick yoghurt (80g)
2 large eggs, separated
¼ teaspoon cayenne pepper
1/8 nutmeg, freshly grated
Pre-heat the oven and baking tray - 200C. Gas Mark 6
You will need a 14cm x 6cm soufflé dish well buttered and a solid baking tray
Begin by heating the butter in a small saucepan, then stir in the chopped spring onion and cook gently for 5 minutes. Then remove from the heat and stir in the soured cream and yoghurt.
Now beat the egg yolks into the sauce and add the potatoes. Lastly stir in all but 1 dessertspoon of each of the cheeses then season with a little salt and about ¼ teaspoon of cayenne pepper and the nutmeg then transfer to a large bowl.
In a separate (grease-free) bowl, whisk the egg whites until soft peaks (see Video Techniques: Perfect Egg Whites) and stir one large spoonful into the cheese mixture to slacken it and make it easier to fold in the rest using a large kitchen spoon.
Taste for seasoning before carefully folding in the remaining egg white.
Pour the whole lot into the soufflé dish with the help of a rubber spatula and sprinkle the top with the extra Cheddar and Parmesan and a sprinkling of cayenne pepper.
Place on the pre-heated baking tray and bake near the centre on the oven for 30 minutes or until well risen and golden brown.
Serve as soon as possible (it will shrink a bit on the way to the table but even when shrunken and cold it still tastes good!).