Broccoli Au Gratin recipe. 1 head of broccoli floret Kosher salt 4 tablespoons (1/2 stick) unsalted butter 3 tablespoons all-purpose flour 2 cups hot milk 1/2 teaspoon freshly ground black pepper 1/4 teaspoon grated nutmeg 3/4 cup freshly grated Gruyere 1/2 cup freshly grated Parmesan 1/4 cop of bread crumbs White sauce. - Melt 2 tbs of butter then add all-purpose flour all at one, mix well. - add 2 cups of hot milk stir until it gets thicken. - Turn of the heat then add salt, ground black pepper, nutmeg and Gruyere cheese, mix well. In a baking tray. - add broccoli and pour the white sauce on top. - Sprinkle over the top with bread crumbs mixed with parmesan cheese. - Drizzle with melt butter for a nice brown and crusty texture. Bake at 375 f for 25 mins.