Bring a large pot of well-salted water to a rolling boil.
Boil macaroni until just shy of al dente. Reserve 1/2 cup pasta water, then drain.
Stir panko with melted butter and Parmesan in a skillet; toast until lightly golden. Set aside.
Melt the butter for the sauce in a medium pot over medium heat.
Whisk in flour and cook, stirring, until blond and nutty, about 2 minutes.
Gradually whisk in warm milk and cream. Simmer, whisking, until thick enough to coat a spoon.
Season the sauce with salt, pepper, Dijon, garlic powder, and nutmeg. Adjust salt to taste.
Take off heat. Stir in Gruyere and cheddar until smooth and glossy.
Fold in drained pasta. Loosen with a splash of reserved pasta water if needed.
Serve hot, topped with toasted crumbs and a sprinkle of chives or parsley.
Notes
Variation: Stir in cooked bacon bits or caramelized onions with the pasta for a smokier, savory twist. Try a pinch of smoked paprika or a drizzle of truffle oil before serving.Storage: Refrigerate leftovers in an airtight container up to 3 days. Rewarm gently with a splash of milk to restore creaminess.This recipe is an original creation inspired by classic Easy Gruyere Mac and Cheese flavors. All ingredient ratios and instructions are independently developed.