3 tablespoons butter, plus extra for greasing the dish
1/4 cup grated Parmesan cheese, divided
1 shallot, minced (can substitute scallions)
3 tablespoons all-purpose flour
1 cup whole milk (plant milk works)
3 large eggs
1/4 teaspoon cream of tartar
4 ounces (1 cup) Gruyere, Cheddar, Swiss or Gouda cheese
1/2 teaspoon salt or to taste
1/4 teaspoon pepper
1/4 teaspoon Dijon mustard
Large pinch of nutmeg
1/2 teaspoon pure vanilla extract
Place an oven rack in middle position and heat oven to 350 degrees. Grease the bottom and sides of an 8-1/2 by 4-1/2-inch glass loaf pan, a 1-1/2 quart soufflé dish, or a 1-1/2 quart ovenproof pot. Sprinkle 2 tablespoons Parmesan into the pan and shake to coat evenly.
Melt 3 tablespoons butter in a medium saucepan or skillet, over medium heat. Add shallot and cook until softened, about 2 minutes. Stir in flour and cook until golden, about 1 – 2 minutes. Slowly whisk in milk. Bring to a simmer and cook, whisking until thickened and smooth, about 1 -2 minutes. Remove from heat, whisk in cheese, salt, pepper, mustard, nutmeg and vanilla. Transfer mixture to a large bowl. Whisk in egg yolks until completely incorporated and set aside.
In a separate bowl, beat egg whites and cream of tartar (with an electric mixer at medium-high speed or whisk by hand) until stiff peaks form.
Working with a quarter of the whipped egg whites at a time, gently fold them into the yolk mixture until almost no white streaks remain. Pour mixture into prepared pan and sprinkle with remaining 2 tablespoons Parmesan. Bake until top is nicely browned and center jiggles slightly, 25 – 30 minutes. Bring the soufflé straight from the oven to the table. Serves 4