These are a wonderful starter for a special occasion. Jerusalem artichokes have an earthy, nutty flavour that makes a great soufflé.
Preheat the oven to 200°C/400°F/gas mark 6 and place a baking sheet in it. Use half the butter to grease four 200 ml (7 fl oz) soufflé dishes and then dust them with Parmesan.
Put the artichokes in a pan with the water, cover and bring to the boil. Simmer for 10-15 minutes, until tender. Drain, reserving the cooking water, and mash the artichokes to a purée. Place the purée in a clean pan and stir over a very low heat to dry it out.
Melt the remaining butter in a pan, stir in the flour and cook gently for a few minutes. Gradually stir in the milk and the reserved cooking liquid, then bring to the boil, stirring all the time, so the sauce thickens. Remove from the heat and add the artichoke purée, then the egg yolks. Season generously with salt, pepper and cayenne. Whisk the egg whites until stiff. Beat one third of the whites into the purée mixture, then fold in the rest. Fill the soufflé dishes with the mixture, place on a baking sheet and bake for 20-25 minutes, until puffed and golden but still slightly creamy in the centre. Serve immediately.