- Position a rack in the upper third of an oven and preheat to 375°F. Butter a shallow 2-quart baking dish.
- In a saucepan over medium heat, warm the milk until bubbles begin to form around the edges of the pan. Keep warm.
- To make the roux, in another medium saucepan over medium heat, melt the butter. When the foaming subsides, add the flour and cook, stirring constantly with a whisk or wooden spoon, until the flour and butter thicken into a paste and smell fragrant, about 1 minute. Do not let the roux brown. Slowly whisk in the milk until smooth and blended. Bring the sauce to a boil over medium heat, stirring constantly and scraping the bottom and sides of the pan to prevent lumping and scorching, then reduce the heat to low.
- Using the clove, attach the bay leaf to the onion and add it to the sauce. Cook, stirring occasionally, until thickened, about 30 minutes. Remove and discard the onion, add 1 cup of the cheese and stir until blended. Season with salt, white pepper and nutmeg, add the sherry and stir until blended.
- Meanwhile, bring a large pot three-fourths full of water to a boil over high heat. Add 1 tablespoon salt and the macaroni and cook according to the package instructions until al dente (tender but firm to the bite). Drain well.
- Transfer the macaroni to the prepared dish. Spoon the sauce over the macaroni, scatter the remaining 1 cup cheese over the top and sprinkle the bread crumbs over the cheese. Bake, uncovered, until lightly browned and bubbling, 35 to 40 minutes. Serve immediately.
- Serves 4 to 6.