Bring 4 cups of water to a rolling boil in a medium pot. Add 1 tablespoon salt. Add 1½ cups elbow macaroni and cook until just shy of al dente (about 7–8 minutes, check package directions). Reserve ½ cup of the pasta cooking water, then drain the pasta and set aside.

Cheese Sauce

Make a roux

In the same pot or a separate medium saucepan, melt 3 tablespoons unsalted butter over medium heat. When butter is foaming but not browned, add 3 tablespoons all-purpose flour and whisk constantly for 1–2 minutes until the raw flour scent cooks off and the mixture is pale golden.

Add milk and cream

Gradually whisk in 2 cups whole milk and ½ cup heavy cream, adding a small splash at a time to avoid lumps. Bring the mixture to a gentle simmer while whisking. Cook 3–4 minutes until it thickens enough to coat the back of a spoon.

Season the béchamel

Stir in 1 teaspoon Dijon mustard, ½ teaspoon garlic powder, 1 teaspoon fine sea salt, ½ teaspoon freshly ground black pepper, and 1/8 teaspoon freshly grated nutmeg. Taste and adjust seasoning carefully; cheeses will add salt.

Add cheeses

Lower heat to low. Add 1 cup shredded Gruyère, 1 cup shredded white cheddar, and ½ cup finely grated Parmigiano-Reggiano in small handfuls, stirring after each addition until fully melted and the sauce is smooth. If the sauce seems too thick, whisk in 1–3 tablespoons reserved pasta water until desired consistency is reached.

Finish with truffle oil

Remove sauce from heat and stir in 1 teaspoon white truffle oil. Mix well to distribute the truffle aroma through the sauce.

Add the drained pasta to the sauce and toss gently to coat, ensuring all pasta is evenly covered. If needed, add another tablespoon or two of the reserved pasta water to reach a creamy texture.

Topping (optional)

Prepare topping

Preheat the broiler (or oven to 400°F / 200°C if you prefer baking). In a small bowl, combine ½ cup panko breadcrumbs, 1 tablespoon melted butter, 1 teaspoon chopped parsley, and 2 tablespoons extra grated Parmigiano-Reggiano. Toss until crumbs are evenly coated.

Finish under broiler

Transfer the mac and cheese to an ovenproof dish if not already in one. Sprinkle the breadcrumb mixture evenly over the top. Broil on the top rack for 1–3 minutes, watching closely, until the crumbs are golden brown. Alternatively, bake at 400°F (200°C) for 8–10 minutes.

Finish & Serve

Remove from oven or pan. Drizzle ½ teaspoon extra white truffle oil over the top for enhanced aroma. Grind additional black pepper to taste and sprinkle 1 teaspoon chopped chives or parsley if using.

Let rest 2–3 minutes so the sauce settles, then serve warm. Store leftovers covered in refrigerator for up to 3 days; reheat gently with a splash of milk.