Preheat the oven to 200°C (400°F). Generously butter six 8-ounce ramekins with Unsalted Butter and evenly dust the insides with grated Parmesan Cheese; tap out any excess.
Make the base: in a medium saucepan, melt 2 tablespoons of unsalted butter over medium heat, then whisk in Plain Flour and cook for 1–2 minutes to form a roux without browning.
Slowly whisk in warm Whole Milk a little at a time until smooth, then continue cooking and whisking until the sauce is thick and coats the back of a spoon.
Remove the pan from the heat and stir in grated Gruyère Cheese and the remaining Parmesan until fully melted and silky.
Season the cheese sauce with Salt, freshly ground White Pepper, a light grating of Nutmeg, and a small pinch of Cayenne Pepper to taste; allow the mixture to cool slightly so it won’t cook the eggs.
Separate the Eggs, adding the yolks one at a time into the warm (not hot) cheese sauce and stirring until smooth. Reserve the whites for whipping.
Whip the reserved egg whites with a pinch of salt until they hold soft to medium peaks. To lighten the base, fold one large spoonful of the whipped whites into the cheese sauce to loosen it, then gently fold in the remaining whites in two additions—use a spatula and fold with an under-and-over motion to preserve air.
Spoon the soufflé mixture into the prepared ramekins, filling them nearly to the top. Smooth the surface and run your thumb around the inside rim of each ramekin to help the soufflés rise evenly. Place the ramekins in a roasting pan and add hot water to the pan until it reaches halfway up the sides of the ramekins (water bath).
Bake in the preheated oven for 20–25 minutes, or until the soufflés have risen, are golden on top, and the centers are just set. Avoid opening the oven door during baking.
Serve immediately—these are best enjoyed straight from the oven while puffed and airy.
