Broccoli Gratin - Cookingwithdia

1/4 cup unsalted butter, plus more for the baking dish

3 tablespoons all-purpose flour

1 1/2 cups whole milk

1 1/2 teaspoons kosher salt, plus more as needed

Pinch freshly grated nutmeg

Freshly ground black pepper

2 pounds broccoli (about 4 heads), cut into small florets (about 8 cups)

1 cup grated sharp Cheddar (about 4 ounces)

1/2 cup fresh bread crumbs

Place a rack in the middle of the oven and preheat to 450 degrees F. Butter an 8-by-8-by-2-inch baking dish or an 8-cup gratin dish.
Melt 3 tablespoons of the butter in a medium saucepan over medium heat. Whisk in the flour until smooth. Cook, stirring, for 1 minute. Add the milk, 1 1/2 teaspoons salt, and nutmeg and bring to a boil while whisking constantly. Lower the heat and simmer, stirring occasionally, until the white sauce is thickened, about 10 minutes. Season with pepper. Remove from the heat.
Meanwhile, bring about 1-inch of water to a boil in a large saucepan and set up a collapsible steamer on top. Put the broccoli in the steamer and season with salt. Cover, and steam until crisp-tender, about 5 minutes. Put the broccoli in the prepared dish, sprinkle with half of the cheese and pour on the sauce. Cover with the remaining cheese.
Melt the remaining 1 tablespoon butter in a medium skillet over medium-high heat. Add the bread crumbs and cook, stirring, until lightly browned, about 2 minutes. Cover the gratin with the bread crumbs. Bake until lightly browned and bubbly, about 20 minutes. Serve immediately.