Topping
2 Tbsp. unsalted butter
2 Tbsp. extra-virgin olive oil
2 cups panko
2 large garlic cloves, finely chopped
2 oz. finely grated Parmesan (about ½ cup)
½ tsp. Diamond Crystal or ¼ tsp. plus ⅛ tsp. Morton kosher salt
Macaroni and sauce
2 tsp. Diamond Crystal or 1 tsp. Morton kosher salt, plus more
1 lb. dried elbow macaroni
½ cup (1 stick) unsalted butter, plus more for baking dish
6 Tbsp. all-purpose flour
4 cups whole milk
¾ cup heavy cream
½ tsp. ground white pepper
1½ Tbsp. mustard powder
16 oz. coarsely grated extra-sharp cheddar cheese (about 6 cups)
2 oz. grated Parmesan (about ½ cup)
Topping
Step 1
Melt 2 Tbsp. unsalted butter In a large skillet on the stovetop over medium heat. Add 2 Tbsp. extra-virgin olive oil, stirring, until butter foam subsides. Add 2 cups panko and 2 large garlic cloves, finely chopped; cook, stirring, until crumbs are golden brown, 4–6 minutes. Transfer crumbs to a medium bowl, stir in 2 oz. finely grated Parmesan (about ½ cup) and ½ tsp. Diamond Crystal or ¼ tsp. plus ⅛ tsp. Morton kosher salt, and set aside.
Macaroni and sauce
Step 2
Bring a large pot of salted water, covered, to a boil over high heat. Add 1 lb. dried elbow macaroni and cook, uncovered, until just al dente (avoid overcooking). Drain par-cooked macaroni and set aside (do not rinse).
Step 3
Place rack in middle of oven; preheat oven to 400°F. Grease a 13x9” baking dish with unsalted butter.
Step 4
Melt ½ cup (1 stick) unsalted butter in a large wide pot over medium-low heat. Sprinkle 6 Tbsp. all-purpose 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 4 cups whole milk and ¾ cup heavy 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. Diamond Crystal or 1 tsp. Morton kosher salt, ½ tsp. ground white pepper, and 1½ Tbsp. mustard powder. Add 16 oz. coarsely grated extra-sharp cheddar cheese (about 6 cups) and 2 oz. grated Parmesan (about ½ cup) in three batches, whisking until each addition is melted before adding more. Remove from heat.
Step 6
Add drained macaroni to pot with cheese sauce and stir well to coat. Transfer macaroni mixture to prepared baking dish and place on a rimmed baking sheet. Sprinkle panko topping evenly over macaroni and bake until golden and bubbling, 18–22 minutes. Let baked mac and cheese cool 15 minutes before serving.