Baked Breaded Cauliflower

INGREDIENTS

• 1/2 teaspoon freshly grated nutmeg
• 6 large scallions, trimmed and finely chopped (white part only)
• 1 large cauliflower (about 3 pounds), trimmed of leaves and coarse bottom stem, then cooked until crisp-tender (see Note above)
• 1/2 teaspoon freshly ground black pepper
• 1/2 cup freshly grated Parmigiano Reggiano (see Tip above)
• 1/3 cup moderately coarse dry bread crumbs mixed with 2 tablespoons freshly grated Parmigiano Reggiano and 1 tablespoon melted unsalted butter (Topping)
• 2 1/2 tablespoons unsalted butter
• 3/4 teaspoon salt
• 2 cups half-and-half, at room temperature
• 3 tablespoons all-purpose flour