Ingredients

5 large eggs

1 ounce Parmesan cheese

1 1/2 ounces Gruyère cheese

1 small shallot (about 2 ounces)

10 ounces frozen chopped spinach, or 12 ounces baby spinach

3 tablespoons unsalted butter, plus more for the baking dish

3 tablespoons all-purpose flour

1 cup whole or 2% milk

1 teaspoon kosher salt

1/4 teaspoon freshly ground black pepper

1/8 teaspoon freshly grated nutmeg

Pinch cayenne pepper

1/8 teaspoon cream of tartar

Instructions

Step 1: Separate all 5 egg whites into a stand mixer bowl or large bowl. Place 4 egg yolks in a small bowl and reserve the remaining yolk for another use. Let eggs come to room temperature for at least 20 minutes. Meanwhile, arrange a rack in the middle of the oven and preheat to 400ºF, removing any racks above.

Step 2: Butter a 6- to 8-cup soufflé dish or 2-quart baking dish generously. Finely grate 1 ounce Parmesan cheese and sprinkle 2 tablespoons evenly on the bottom and sides of the dish.

Step 3: Grate Gruyère cheese on large holes of a box grater. Finely dice the shallot.

Step 4: If using frozen spinach, defrost in microwave in 1-minute bursts, stirring between each, about 2 1/2 to 3 minutes. If using baby spinach, blanch in boiling water until wilted, then drain and rinse with cold water.

Step 5: Transfer spinach to a strainer and squeeze out all excess moisture by hand. Finely chop fresh spinach if used.

Step 6: Melt 3 tablespoons butter in a small saucepan over medium heat. Add shallot and cook until softened, about 3 minutes. Stir in flour and cook, whisking constantly, for about 1 minute.

Step 7: Gradually whisk in milk, stirring until flour dissolves. Add salt, pepper, nutmeg, and cayenne. Simmer for 2 to 4 minutes, stirring constantly.

Step 8: Remove from heat and whisk in egg yolks one at a time until fully incorporated. Stir in Gruyère, spinach, and remaining Parmesan until evenly combined. Transfer to a large bowl.

Step 9: Add cream of tartar to egg whites and beat until firm, glossy peaks form (3 to 4 minutes).

Step 10: Gently fold about 1/4 of the egg whites into the spinach mixture to lighten it. Then fold in the remaining egg whites gently, just until no large streaks remain.

Step 11: Pour the mixture into the prepared dish and smooth the top. Tap the dish gently on the counter to settle the batter.

Step 12: Place in the oven and immediately reduce temperature to 375ºF. Bake 40 to 45 minutes for a soufflé dish or about 30 minutes for a regular baking dish, until puffed and golden brown. Avoid opening the oven door early.

Step 13: Serve immediately as the soufflé will deflate quickly.

Tips & Variations

For best results, make sure to squeeze out as much moisture from the spinach as possible to prevent a soggy soufflé.

Use a serrated knife to gently cut and serve the soufflé to preserve its delicate structure.

Substitute Gruyère with Sharp Cheddar or Emmental for a different flavor profile.

Add a pinch of smoked paprika for a subtle smoky note.

FAQs

Can I use fresh spinach instead of frozen?

Yes, fresh baby spinach can be used. Blanch it briefly in boiling water, then drain, rinse with cold water, squeeze out moisture, and finely chop before adding.

What if I don’t have cream of tartar?

Cream of tartar helps stabilize the egg whites. If unavailable, you can use a few drops of lemon juice or white vinegar as a substitute, or simply beat the whites until they hold firm peaks.