Bring a large pot of water to a rolling boil (about 4 cups water per 12 oz pasta is sufficient for this recipe). Add 1 tablespoon kosher salt. Add the elbow macaroni and cook until very al dente, 1–2 minutes shy of package directions (usually 7–8 minutes depending on brand). Stir occasionally to prevent sticking.

Reserve 1/2 cup of the starchy pasta cooking water, then drain the pasta in a colander and set aside. Do not rinse.

Cheese Sauce (Roux + Milk)

Make a roux

In a medium heavy-bottomed saucepan set over medium heat, melt 4 tablespoons unsalted butter. Once foaming, add 4 tablespoons all-purpose flour and whisk constantly for 1–2 minutes until the mixture is golden and smells slightly nutty (this cooks the raw flour taste).

Add milk and cream

Gradually whisk in 2 cups whole milk and 1 cup heavy cream, pouring slowly to avoid lumps. Increase heat to medium-high and continue whisking until the mixture comes to a gentle simmer and thickens slightly, about 4–5 minutes.

Season

Reduce heat to low. Whisk in 1 teaspoon dry mustard powder, 1 teaspoon Worcestershire sauce, 1 teaspoon ground black pepper, and 1/2 teaspoon fine salt. Taste and adjust seasoning — the sauce should be slightly savory and tangy to balance the cheese.

Add cheeses

Remove the saucepan from the heat. Add the grated cheeses in two additions: stir in 2 cups sharp cheddar and 1 cup medium cheddar, whisking after each addition until fully melted and smooth. Then fold in 1 cup grated Gruyère or fontina (if using) until incorporated. If the sauce is too thick, whisk in up to 1/4 cup of the reserved pasta water to loosen to a saucy consistency.

Combine and Bake (or Stove Finish)

Combine pasta and sauce

Add the drained pasta to the cheese sauce and gently fold until every piece is coated. If the mixture seems dry, add more reserved pasta water, 1 tablespoon at a time, until silky and well-coated.

Stove-top finish (creamy, no-bake)

For a creamy, not-baked mac & cheese: return the saucepan to very low heat for 1–2 minutes to warm through (do not boil). Serve immediately, garnished with chopped parsley and a light sprinkle of smoked paprika if desired.

Bake with topping (baked)

Preheat the oven to 375°F (190°C). Transfer the sauced pasta to a 9x13-inch baking dish (or equivalent).

Topping (optional)

Prepare topping

In a small bowl, combine 1 cup panko breadcrumbs, 2 tablespoons melted butter, 2 tablespoons grated Parmesan, and 1/4 teaspoon smoked paprika. Toss until the crumbs are evenly moistened.

Evenly sprinkle the breadcrumb mixture over the assembled mac & cheese in the baking dish.

Bake uncovered in preheated 375°F (190°C) oven for 20–25 minutes, until the topping is golden brown and the sauce is bubbling around the edges. If you want a darker crust, broil for 1–2 minutes while watching closely.

Remove from oven and let rest 5–10 minutes before serving. Garnish with chopped fresh parsley.