Step 1

Preheat the oven to 375 F. Bring a large pot of salty water to boil. Boil the cauliflower florets until beginning to soften, but farm from tender, about 5 minutes.

Step 2

In the meantime, melt 2 tablespoons of the butter in a sauce pan, then stir in the flour. Cook for 2-3 minutes, stirring often and removing any lumps. Add the warm milk (little by little at first), whisking constantly. Bring to a boil and cook until the mixture thickens, 1 to 3 minutes. Remove from the heat and add 1 teaspoon salt, the pepper, 1/2 cup of each cheese, and nutmeg. Stir well to incorporate.

Step 3

Pour 1/3 of the sauce into an 8 x 11 inch baking dish, then add the cauliflower pieces. Cover with the remaining sauce, then top with a mixture of the bread crumbs and remaining Gruyère. Melt the remaining two tablespoons butter and drizzle over the top. Bake for 25-30 minutes, until the top is browned. Hit it with a broiler to really crisp it up.