2 tablespoons unsalted butter, plus more for baking dish
    2 tablespoons extra-virgin olive oil
    2 cups panko (Japanese breadcrumbs)
    2 large garlic cloves, minced
    2 ounces finely grated Parmesan (about 1/2 cup)
    1/2 teaspoon kosher salt

For the macaroni and sauce:

    2 teaspoons kosher salt, plus more
    1 pound dried elbow macaroni
    1/2 cup (1 stick) unsalted butter
    6 tablespoons all-purpose flour
    4 cups whole milk
    3/4 cup heavy cream
    1/2 teaspoon ground white pepper
    1 1/2 tablespoons mustard powder
    16 ounces coarsely grated extra-sharp cheddar (about 6 cups)
    2 ounces grated Parmesan (about 1/2 cup)

Special equipment:

    9- by 13-inch baking dish