Preheat the oven to 200°C, gas mark 6; grease 6 x 250ml ramekins with the softened butter, then coat with 30g grated cheese. Place the ramekins on a baking tray and chill.
Melt the remaining 30g butter in a pan over a medium heat and add the flour, stirring constantly to make a roux, for about 1 minute. Gently add the milk; stir constantly to incorporate. Let the sauce bubble for a few minutes, then add the remaining gruyère; continue stirring until the cheese has melted and the mixture is smooth. Remove from the heat and leave to cool for a few minutes. Stir the egg yolks into the mixture; season to taste, then add the nutmeg.
Whisk the egg whites with a pinch of salt till they form soft peaks; fold half into the sauce very gently, until combined; repeat with the other half, keeping the mix airy. Divide between the ramekins and level the tops with a spatula. Run the tip of your thumb around the inside of each dish to make a small gap between the soufflé and dish – this will help it rise.
Bake the soufflés on the baking tray for 15 minutes. They should be well risen and golden – but don’t open the oven to check! Serve immediately with the salad. And if the soufflés collapse, laugh…