Preheat the oven to 400°F. Generously butter four 6-ounce ramekins with butter and coat the inside of each ramekin with grated Parmesan cheese, tapping out any excess.

Separate 4 large eggs, placing the egg yolks in one bowl and the egg whites in a large clean mixing bowl.

In a medium saucepan, melt 2 tablespoons unsalted butter over medium heat.

Stir in 2 tablespoons all-purpose flour and cook, stirring constantly, for 1–2 minutes to create a roux.

Gradually whisk in ½ cup whole milk and cook, stirring constantly, for 2–3 minutes until the mixture thickens and coats the back of a spoon.

Remove the saucepan from the heat and stir in ½ cup grated Gruyère cheese, ¼ cup grated Parmesan cheese, ¼ teaspoon salt, and ? teaspoon ground black pepper until smooth and melted.

Whisk the egg yolks until light and frothy. Slowly pour the cheese mixture into the egg yolks while whisking constantly to prevent scrambling.

Using an electric mixer, beat the egg whites with ? teaspoon cream of tartar until stiff peaks form.

Gently fold one-third of the egg white mixture into the cheese mixture to lighten it. Then carefully fold in the remaining egg whites until just combined, being careful not to overmix.

Divide the soufflé batter evenly among the 4 prepared ramekins, filling them almost to the top.

Place the ramekins on a baking sheet and bake for 12–15 minutes, until the soufflés have risen and are golden brown on top.

Serve immediately, optionally garnished with a light dusting of grated Parmesan cheese or fresh herbs if desired.