3 large eggs, separated
Kosher salt and freshly ground black pepper
2 ounces (55g) grated Gruyère or cheddar cheese, divided
Minced fresh chives (optional)
1 tablespoon (15g) unsalted butter
In a medium bowl, beat egg yolks with a generous pinch of salt and some freshly ground black pepper until well mixed.
In a separate large mixing bowl, using a whisk, electric hand blender, or stand mixer fitted with the whisk attachment, beat egg whites until firm, glossy peaks form.
Add half of the beaten egg whites to yolks and stir well until whites are thoroughly combined and soufflé base has a looser consistency. Mix in half the cheese as well as the chives, if using. Add remaining beaten whites, and, using a silicone spatula, gently fold them into the soufflé base just until well combined.