- 3 tablespoons unsalted butter plus more, room temperature, for ramekins
- 4 tablespoons finely grated Parmesan, divided
- 3 tablespoons all-purpose flour
- 1 cup cold whole milk
- 1 cup grated Gruyère, divided
- Pinch of freshly grated nutmeg
- Kosher salt, freshly ground pepper
- 4 large eggs, yolks and whites separated
- 1/4 teaspoon xanthan gum (optional)
- Special equipment: Four 8-ounce ramekins
- Preheat oven to 400°F. Brush ramekins with butter and place on a foil-lined baking sheet; sprinkle ramekins with 2 tablespoons Parmesan (total). Chill for 20 minutes or, covered, up to 1 day.
- Melt 3 tablespoons butter in a small saucepan over medium heat. Add flour; whisk constantly for 30 seconds. Gradually whisk in milk; increase heat and bring to a boil, whisking constantly. Add remaining 2 tablespoons Parmesan and 1/2 cup Gruyère; stir until melted. Add nutmeg and season with salt and pepper. Transfer béchamel to a medium bowl and cover with plastic wrap; set aside.
- Place egg whites in a large bowl. Stir in a pinch of salt and xanthan gum, if using. Using an electric mixer, beat egg whites until firm but not stiff, 3-4 minutes.
- Stir egg yolks into béchamel. Gently stir in 1/4 of beaten egg whites to loosen béchamel base, then gently fold in remaining egg whites just to combine, taking care not to deflate.
- Divide mixture among ramekins; sprinkle with 1/2 cup Gruyère. Run your finger around inside lip of ramekins, cleaning edges. Bake until soufflés rise, centers are set, and cheese is golden brown, 18-22 minutes. Serve immediately.