Bring a pot of salted water to a boil. Pour in the macaroni and cook until very al dente, about 7 minutes, or as directed per the instructions on the package of pasta.
In a bowl, toss together the melted butter, bread crumbs and salt. Place the hatch chiles on the grates of a gas range and turn the heat to high. Rotate the chiles until they're evenly charred. Immediately transfer them to a cutting board and using the blade of a knife, scrap the charred skin off of the peppers. Dice the softened peppers and set them aside. Beware that these are spicy so cut them into a small dice and don't rub your eyes!
To a medium saucepan set over medium-low heat, add the butter and flour. Cook the roux, until the butter melts and a paste forms. Whisk in the milk and bring the sauce to a very slight boil, whisking the entire time, and cook for about 1 minute. Turn the heat off and allow the milk mixture to cool slightly, about a minute or two. Stir in the cheeses and pepper. Add the salt and adjust according to your liking. This will largely depend on how salty the cheese you just added is.
In a large bowl, add the macaroni and pour the cheesy sauce on top. Stir the pasta until it's completely coated in the sauce. Add the hatch chiles and mix. Transfer the macaroni and cheese to a 9 x 13-inch baking dish. Top with the panko bread crumb mixture and transfer to the oven to bake for 15 minutes. Place the macaroni under the broiler to bake for an additional 5 minutes, until the top is golden brown. Serve immediately.
*Hatch chiles are pretty spicy so I recommend dicing them very small. Use two hatch chiles if you want a moderate kick. If you like things spicy, go with three! I used three and was like, dang, but I was into it.