1. For the soufflé: Preheat the oven to 200C/180C fan/gas 6. Melt 65g of the butter in a small saucepan set over low heat. Using a small wire whisk, stir in the flour and cook gently for 2-3 minutes, stirring continuously.
2. Take the pan off the heat and leave the roux to cool slightly. Bring the milk to the boil, then pour it slowly over the cooled roux, whisking all the time. Set the pan over high heat and, stirring continuously, bring the mixture to the boil and cook for 3 minutes.
3. Take the pan off the heat and stir in the egg yolks. Season to taste with salt and freshly ground white pepper. Pour the soufflé mixture into a wide-mouthed bowl and dot the surface with 1 tbsp of the butter, cut into small pieces, to prevent a skin from forming. Set aside to cool to room temperature.
4. Meanwhile, chill 8 round 8cm tartlet tins in the refrigerator or freezer for a few minutes. Remove and immediately grease them generously with softened butter and arrange on a baking sheet.
5. To assemble: Beat the egg whites with a pinch of salt until they form stiff peaks. Using a whisk, quickly beat one-third of the egg whites into cooled soufflé mix, then, using a spatula, carefully fold in the remainder to completely blend them. Using a tablespoon, heap the mixture into the tartlet tins on the baking tray.
6. Pour the cream into a saucepan. Lightly salt the cream then warm gently on the hob, over a low heat without letting it boil. Pour the cream into a warmed gratin dish that is big enough to hold all 8 tartlet tins.
7. To cook: Bake the tray of soufflés in the preheated oven for 3 minutes, until the tops begin to turn golden. Remove from the oven and protecting your hands with a cloth, turn out each soufflé into the gratin dish of warm cream. Sprinkle over the Gruyere or Emmental and return to the oven for 5 minutes. The soufflés must be taken immediately to the table; serve them with a spoon and fork, taking care not to crush them.