1. For the topping: Pulse bread, butter, salt, and pepper in food processor until mixture resembles coarse crumbs, about ten 1-second pulses; set aside.

2. For the filling: Adjust oven rack to middle position; heat oven to 450°F. Bring 4 quarts water to boil in Dutch oven or stockpot over high heat. Add 1 tablespoon salt and broccoli; cook until exterior is tender but interior is still slightly crunchy, about 3 minutes. Drain broccoli in colander; leave in colander while preparing sauce.

3. Heat butter in large skillet over medium heat; when foam subsides, add shallot and cook until softened, about 2 minutes. Add garlic and cook until fragrant, about 30 seconds; stir in flour until combined, about 1 minute. Whisk in cream and broth; bring to boil. Stir in nutmeg, cayenne, remaining 1/4 teaspoon salt, pepper, thyme, and two-thirds cheese until incorporated. Off heat, gently stir in broccoli until evenly combined. Transfer mixture to 11 x 7-inch (2-qt) gratin dish. Sprinkle remaining one-third cheese evenly over surface, then sprinkle evenly with bread crumb topping. Bake until golden brown and sauce is bubbling around edges, 10 to 12 minutes. Serve immediately.

Serves 6