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.
Copyright 2005 Television Food Network, G.P. All rights reserved.