Step 1

Preparation Preheat oven to 400°F with rack in the middle of oven. Butter the baking dish.

Step 2

Make the topping: In a large skillet over medium heat, heat butter and oil until butter foam subsides. Add panko and garlic; cook, stirring, until crumbs are golden brown, 4–6 minutes. Transfer crumbs to a medium bowl, stir in Parmesan and salt, and set aside.

Step 3

Prepare the macaroni and sauce: Set a large, covered pot of salted water over high heat to boil. Add macaroni and cook until just al dente (avoid overcooking). Drain macaroni and set aside.

Step 4

In a large wide pot over medium-low heat, melt the butter. Sprinkle flour over butter, whisking to incorporate and make a roux. Cook, stirring constantly with a wooden spoon, until roux is light golden, about 4 minutes. Gradually pour in milk and cream, whisking constantly to incorporate and make a béchamel sauce. Raise heat to medium-high and bring sauce to a low boil, whisking constantly. Reduce to a simmer, whisking occasionally, and cook until béchamel sauce is thick and coats the back of a spoon, about 3 minutes more.

Step 5

Add 2 tsp. salt, pepper, and mustard powder. Add the cheeses in three batches, whisking until each addition is completely melted before adding more. Remove from heat.

Step 6

Add the drained macaroni to the pot with the cheese sauce and stir well to coat. Transfer macaroni mixture to the buttered baking dish and place on a rimmed baking sheet. Sprinkle topping evenly over macaroni and bake until golden and bubbling, 18–22 minutes. Let cool 15 minutes before serving.