Serves 2 to 3
3 tablespoons unsalted butter, plus extra for greasing the dish
1/4 cup finely grated Parmesan cheese, plus extra for sprinkling
3 tablespoons all-purpose flour
1 cup scalded milk
1/4 teaspoon nutmeg
Pinch of cayenne pepper
Kosher salt and freshly ground black pepper
4 extra-large egg yolks, at room temperature
1/2 cup grated aged Cheddar cheese, lightly packed
1 package frozen chopped spinach, defrosted and squeezed dry
5 extra-large egg whites, at room temperature
1/2 teaspoon cream of tartar
1. Preheat the oven to 400 degrees. Butter the inside of one 6-to-8-cup soufflé dish (6 1/2 to 7 1/2 inches in diameter x 3 1/2 inches deep) and sprinkle evenly with Parmesan.
2. Melt the butter in a small saucepan over low heat. With a wooden spoon, stir in the flour and cook, stirring constantly, for 2 minutes. Off the heat, whisk in the hot milk, nutmeg, cayenne, 1/2 teaspoon salt, and 1/4 teaspoon black pepper. Cook over low heat, whisking constantly, for one minute, until smooth and thick.
3. Off the heat, but while still hot, mix in the egg yolks. Stir in the Cheddar, the Parmesan, and the spinach, and transfer to a large mixing bowl.
4. Put the egg whites, cream of tartar, and a pinch of salt in the bowl of an electric mixer fitted with the whisk attachment. Beat on low speed for one minute, on medium speed for one minute, then finally on high speed until firm, glossy peaks are formed.
5. Whisk one-quarter of the egg whites into the cheese sauce to lighten, and then fold in the rest. Pour into the prepared soufflé dish, then smooth the top. Draw a large circle on top with the spatula and place in the middle of the oven. Turn the temperature down to 375 degrees. Bake for 30 to 35 minutes (don’t peek!) until puffed and brown. Serve immediately.
NOTE: To make in advance, prepare the recipe through Step 3 (adding the cheeses). You can do this up to 2 hours ahead. Keep mixture covered at room temperature, and then proceed with the recipe just before baking.