Step 1

Arrange a rack in the top third of the oven (about 6 to 8 inches from the broiler element), and heat to 400°F. Meanwhile, bring a large pot of salted water to a boil. Add the gnocchi and cook until al dente, about 3 minutes or according to package instructions. Drain and set aside.

Step 2

Melt the butter in a 10- or 12-inch cast iron or other ovenproof high-sided skillet over medium heat. Sprinkle in the flour and whisk until fragrant, 1 to 2 minutes. While whisking constantly, slowly pour in the milk and continue whisking until smooth. Switch to a wooden spoon and continue cooking, stirring constantly, until the sauce is noticeably thickened and coats the back of the spoon, about 2 minutes.

Step 3

Remove the pan from the heat. Stir in the cheddar one handful at a time until melted and smooth. Stir in the mustard, pepper, salt, paprika, and half the Parmesan. Add the cooked gnocchi and stir gently until the gnocchi is evenly coated with sauce. Top with remaining Parmesan.

Step 4

Bake until the sauce is bubbling, 10 to 12 minutes. Turn on the broiler and broil until the top is golden-brown, 2 to 4 minutes. Remove from the oven and rest for 5 to 10 minutes. Top with basil or parsley before serving.