Bring 4 cups water to a rolling boil in a medium pot. Add 1 tablespoon kosher salt. Add 2 cups elbow macaroni and cook until just shy of al dente (about 1–2 minutes less than package directions), usually 7–8 minutes. Reserve 1/4 cup of pasta cooking water, then drain pasta in a colander and set aside.

Cheese sauce (béchamel-based)

Make the roux

In the same pot or a separate medium saucepan, melt 3 tablespoons unsalted butter over medium heat. Once bubbling and fragrant (about 1 minute), add 3 tablespoons all-purpose flour and stir constantly with a whisk for 1–2 minutes to cook the raw flour taste; do not let it brown.

Add milk and seasonings

Slowly whisk in 2 cups whole milk, a little at a time, scraping the bottom to incorporate the roux. Continue whisking until the mixture is smooth. Add 1 teaspoon dry mustard powder, 1/2 teaspoon paprika, 1/2 teaspoon ground black pepper, and 1/2 teaspoon kosher salt. Bring to a gentle simmer over medium-low heat, whisking frequently, until the sauce thickens enough to coat the back of a spoon (about 4–6 minutes). If sauce becomes too thick, whisk in up to 2 tablespoons reserved pasta water or milk to adjust consistency.

Finish with cheeses

Reduce heat to low. Remove the sauce from direct heat and add 2 cups shredded sharp cheddar, 1/2 cup shredded gruyère (or mild white cheddar), and 1/4 cup grated parmesan in handfuls, stirring or whisking after each addition until fully melted and smooth. Taste and adjust seasoning with additional salt or pepper if needed.

Combine and bake (or stovetop finish)

Add the drained pasta to the cheese sauce and gently fold until evenly coated. If the sauce seems too thick, stir in up to 2 tablespoons reserved pasta water. For a creamy stovetop mac and cheese, serve immediately.

To bake: Preheat oven to 375°F (190°C). Transfer the sauced pasta to a 1.5-quart baking dish, smoothing the top.

Topping (optional) and baking

If using topping, mix 1/2 cup breadcrumbs with 1 tablespoon melted butter and 1 teaspoon chopped fresh parsley until moistened. Sprinkle evenly over the pasta in the baking dish and dust with a little extra parmesan (about 1 tablespoon) if desired.

Bake uncovered for 15–20 minutes, until the topping is golden and the cheese is bubbling. For an extra-brown top, place under the broiler for 1–2 minutes—watch closely to avoid burning.

Remove from oven and let rest 5 minutes before serving to set. Garnish with a pinch of chopped parsley if desired.