Add the onion, bay leaf, and garlic to a large pot over medium heat. Cook for 3-5 minutes, or until fragrant.

Pour in the milk and heat until small bubbles form around the edges but be sure to not burn it. Cover and remove from heat. Let stand for 15 minutes.

Cook the macaroni according to package directions for al dente. Drain and set aside.

Preheat your broiler. When the 15 minutes have passed, strain the milk mixture through a colander over a bowl, reserving the milk and discarding the solids.

Pour 1/2 cup of the warmed milk into a measuring cup. Add two tablespoons flour, whisking to combine.

Add the remaining milk back into a large saucepan over medium heat. Add flour mixture and salt to the milk on the stove, stirring constantly with a whisk. Bring to a boil and cook for one minute, stirring constantly.

Stir in 1/2 teaspoon ground nutmeg.

Remove from heat. Gradually add the cheese cubes to the hot milk, stirring with a spoon until the cheese melts.

Stir in the pasta.

Transfer the pasta to a 2 quart broiler-safe glass or ceramic baking dish. Top with panko and Parmesan cheese.

Broil for 2 minutes or until crispy on top and golden brown.