Preheat the oven to gas 5, 190°C, fan 170°C and butter a pie dish if you haven't got a smart soufflé dish. (This is more than a ramekin full - after all, you're on your own and treating yourself!) Dust the inside with some of the Parmesan.
Put the fish into a pan with some seasoning and cover with the milk. Bring to the boil and simmer for 5 minutes. Take the fish out with a slotted spoon and reserve the milk. Flake the fish, removing any skin and bones. Strain the milk into a jug.
Heat the butter in the pan, stir in the flour and continue to stir until the mixture comes away from the sides of the pan (this cooked mixture is called a roux).
Gradually add the reserved milk, stirring, until you have a smooth sauce. Stir in the grated Emmenthal cheese, followed by the egg yolks and the flaked fish.
In a clean bowl, whisk the egg whites until standing in stiff peaks. Gently fold these into the sauce mixture. Season to taste.
Pour the mixture into the prepared dish and sprinkle with the Parmesan.
Cook for 25 minutes until well risen. Check with a knife or skewer to see if cooked: if the centre is cooked, this will come out clean; if not, cook for a few more minutes.
Souffles are not the nightmare that most people think they are, you just have to be thorough in your preparation. Always take care that your dish(es) are well buttered, as a missing bit might stop the souffle rising. Take your eggs out of the fridge an hour or two before you plan to beat them as they'll then fluff up better, and make sure the bowl you beat in is scrupulously clean as any grease in it can hamper the beating process. Use the side of a metal spoon to mix the beaten eggs into your other ingredients as this will minimise the loss of the previously beaten-in air.
*Inspired by Tony C. featured in the Realfood Cookbook