Instructions

1. 1
   Preheat the oven to 400°F (200°C).
2. 2
   Butter a 6-cup soufflé dish thoroughly, coating it up to the very rim.
3. 3
   Sprinkle the Parmesan cheese inside, swirling to coat the bottom and sides completely.
4. 4
   Melt 3 tablespoons of butter in a saucepan over medium heat.
5. 5
   Whisk in the flour and cook for 1 minute without browning to form a roux.
6. 6
   Slowly pour in the hot milk while whisking constantly.
7. 7
   Cook until the mixture thickens into a dense, smooth white sauce (Béchamel).
8. 8
   Remove from heat and season with salt, pepper , and cayenne.
9. 9
   Whisk the egg yolks into the warm sauce one at a time, blending thoroughly.
10. 10
    Stir in the finely grated Gruyère cheese.
11. 11
    In a pristine bowl, whip the egg whites until they form stiff, upright peaks.
12. 12
    Stir a quarter of the egg whites into the cheese base to loosen it.
13. 13
    Carefully fold in the remaining whites using a rubber spatula.
14. 14
    Pour into the dish, lower oven heat to 375°F (190°C), and bake for 30 minutes without opening the door .