Heat the oven to 425ºF/220ºC and set a shelf low down. Thickly butter the ramekins, freeze them 10-15 minutes and butter them again. Set them on a baking sheet. Separate the eggs and let the all the eight whites come to room temperature.
Put the cream, potato starch and butter in a saucepan and heat gently, stirring with a whisk, until the sauce thickens (just before it simmers). Take it at once from the heat and stir in the egg yolks. Stir in the cheeses, taste and adjust the seasoning.
Stiffly whisk the egg whites by hand or with an electric mixer. If the cheese mixture has cooled, warm it on the stove but do not let it simmer. Add about a quarter of the whipped egg whites and stir until well mixed. Scoop this mixture with a rubber spatula into the remaining whites and fold together as lightly as possible.
Spoon the mixture into the ramekins to fill them to the brim, and run a metal spatula across the top. Run your finger and thumb around the edge to detach the soufflé mixture from the dishes and set them on the baking sheet.
Bake in the heated oven until the soufflés are puffed and brown, 10-12 minutes. Meanwhile prepare serving plates lined with a napkin. Set the ramekins on the napkins and serve the soufflés at once, with a teaspoon for eating.