Creamy Oven-Baked Mac and Cheese

Instructions

1. Heat the oven to 350F. Melt 2 tablespoons of the unsalted butter in a skillet over medium heat, add the panko, and cook, stirring, until the crumbs are golden brown and smell nutty, 6 to 8 minutes. Transfer to a bowl and toss with the Parmesan, fresh thyme, and a pinch of salt.
2. Cook the cavatappi or elbow macaroni in well-salted water until just shy of al dente, then drain and let it sit while you make the sauce. In a saucepan, melt the remaining unsalted butter, add the grated yellow onion and garlic, and cook until fragrant and softened. Sprinkle in the all-purpose flour and cook, whisking, until the raw flour smell is gone and the mixture starts to stick slightly to the pan, about 1 minute.
3. Whisk in the warm whole milk in a few additions, then bring the sauce to a simmer and cook, stirring, until it is thick, smooth, and no longer tastes floury, 6 to 8 minutes. Off the heat, stir in the Gruyere, cheddar, Fontina, mustard powder, nutmeg, cayenne, and a generous pinch of salt until the sauce is glossy and fully melted.
4. Fold in the pasta and transfer it to a greased baking dish. Top with the buttery breadcrumbs and bake until the edges are bubbling and the top is burnished gold, 18 to 20 minutes. Let it rest for 10 to 15 minutes before serving so the sauce sets into creamy spoonfuls instead of running off the plate.