Crispy on the outside, light and moist in the center, this cheese souffle cooked in an enormous copper pot, and accompanied by nothing more than a green salad and a crusty baguette, is an excellent choice for a dinner party.
Heat oven to 425 degrees. Place rack in center. Generously butter bottom and sides of a 2-quart souffle dish with 1 1/2 tablespoons of unsalted butter. In a small bowl, mix together Parmesan cheese and breadcrumbs, and sprinkle in dish, swirling to thoroughly coat the bottom and sides.
Grate Jarlsberg and cheddar cheeses into a small bowl. Cut Saga blue and brie into small chunks. Combine, and set aside.
Melt the remaining 2 1/2 tablespoons of butter in a large saucepan over low heat. Whisk in flour and mustard, and cook, whisking constantly, for 3 to 5 minutes. Slowly whisk in milk, and cook until thick and smooth, an additional 3 to 4 minutes. Remove from heat, and season with salt, pepper, and cayenne pepper. Pour souffle base into a large bowl. Whisk in egg yolks a few at a time until smooth. Stir in cheese until well incorporated.
In the bowl of a heavy-duty electric mixer fitted with the whisk attachment, whip 12 whites on medium-low speed until foamy. Increase the speed to high, and continue whisking until stiff peaks form, about 4 minutes.
Quickly and gently fold the egg whites and nutmeg into the souffle base just until incorporated. Pour into souffle dish, and bake for 30 to 35 minutes. Serve immediately.