4tablespoons unsalted butter, plus 1 tablespoon melted for topping
1/4cup all-purpose flour
3cups whole milk
1/2teaspoon dry mustard
2cups sharp cheddar cheese, shredded
2cups gruyere, shredded
1/2cup Panko bread crumbs
Salt and pepper to taste
Preheat oven to 425F.
Roast jalapeños by placing on an aluminum lined baking sheet and baking for 15-20 minutes, turning half-way though until they develop some color and are tender.
Reduce oven temperature to 350F and grease a medium-sized (3 quart) casserole dish.
Cook the noodles one minute under the directed time indicated on package directions. Strain noodles and set aside.
Melt butter over medium heat in pot used for noodles. Whisk in the flour and cook for 1 minute.
Gradually add in the milk, whisking frequently. Bring the milk mixture to a boil. Once boiling, remove from heat and add in the dry mustard, cheddar cheese, gruyere cheese, jalapeños, and salt and pepper to taste. Stir until combined.
Add in the noodles and stir until everything is well coated in the sauce. Pour into the prepared dish and set aside.
Mix the topping ingredients (panko, parmesan cheese, and 1 tablespoon melted butter) in a small bowl until combined. Sprinkle on top of the noodles in an even layer.
If desired, slice a fresh jalapeño and place slices on top of the bread crumbs and dot with butter.
Bake at 350F for 20 minutes until golden brown and bubbly.