The Loftiest Souffle

Name: The Loftiest Souffle
Ingredients: 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)