Step 1

Arrange a rack in the middle of the oven and heat the oven to 350ºF. Meanwhile, coat a 9x13-inch baking dish with 1 tablespoon of the unsalted butter. Prepare the macaroni and sauce.

Step 2

Shred the following cheeses, placing them all in the same bowl: 8 ounces extra-sharp cheddar, 8 ounces sharp cheddar, 4 ounces smoked Gouda, and 4 ounces pepper Jack. Toss with your hands to combine. If using, cut 4 ounces mozzarella cheese into small cubes and set aside for topping.

Step 3

Peel and halve 1/2 medium yellow onion and place in a small saucepan. Add 5 1/2 cups whole milk and 1 bay leaf. Heat over medium-low heat until steaming but not boiling, 5 to 10 minutes. Meanwhile, bring a large pot or Dutch oven of heavily salted water to a boil.

Step 4

Add 1 pound macaroni to the boiling water and cook 2 minutes less than package directions for al dente, about 6 minutes. Drain the macaroni and rinse with cold water. (Reserve the pot.)

Step 5

When the milk is ready, pour through a strainer into a bowl. Melt the remaining 6 tablespoons unsalted butter in the now-empty pot over medium heat. Add 1/2 cup all-purpose flour and whisk until combined. Continue whisking for another couple minutes to cook the flour until thickened slightly, bubbly, and light golden brown. This is your roux.

Step 6

Quickly whisk the milk into the roux a cup or two at a time. It will thicken up considerably before you get a chance to add all of the milk. Just whisk vigorously with each round of milk and whisk until smooth after all of the milk has been added. Add 2 teaspoons dry mustard, 1 teaspoon smoked paprika, 1 teaspoon kosher salt, 1/2 teaspoon black pepper, 1/4 teaspoon cayenne pepper, and 1/4 teaspoon freshly grated nutmeg, and whisk to combine.

Step 7

At this point you'll have a thin white sauce called a béchamel. If despite your best efforts, you still end up with a few lumps in your sauce, the easiest and fastest way to fix this is to blend the lumps away with an immersion (stick) blender. Lumps gone.

Step 8

Let the béchamel sauce come to a gentle simmer, then reduce the heat to low. Simmer until thick enough to easily coat the back of a wooden spoon, about 10 minutes. Add 2 teaspoons Worcestershire sauce and stir to combine.

Step 9

Remove the pot from the heat. Set aside about 1/3 of the shredded cheeses. Add the remaining shredded cheeses to the sauce and stir until smooth and melted. Taste and season with more salt or spices as needed. Add the macaroni and stir to combine.

Step 10

Melt 1 tablespoon unsalted butter in a medium frying pan over medium heat. Add 1/2 teaspoon smoked paprika and cook until fragrant. Add 1/4 cup panko breadcrumbs and cook, stirring often, until golden-brown, about 1 minute. Remove from the heat.

Step 11

Transfer half of the macaroni and cheese to the baking dish and spread into an even layer. Sprinkle with half of the reserved cheeses. Repeat layering the remaining macaroni and cheese and remaining shredded cheeses. Press the reserved mozzarella cheese cubes into the casserole if using. Sprinkle with the panko breadcrumbs if using.

Step 12

Bake until bubbly and golden-brown, 30 to 40 minutes. Let cool for 5 to 10 minutes before serving.