Optional: ¼ cup panko bread crumbs (plus two additional butter to toast bread crumbs)
Preheat oven to 350.
Prep: Grate cheddar and pepper jack cheeses. Dice Muenster cheese into small cubes.
Butter a large casserole dish or cast iron skillet.
If using bread crumb topping: Melt 2 tbsp butter and toss with the breadcrumbs in a small pan to brown and set aside.
Begin boiling heavily salted water for the noodles. Cook macaroni noodles in boiling water until slightly undercooked (7-8 minutes)
Begin making the bechamel sauce while the noodles cook. In a small saucepan, add 5 cups milk, peeled onion (cut in half), and the bay leaf. On medium low heat, gently warm the milk until it is steaming hot but not boiling, then reduce to simmer. Steep the onion and bay leaf for 10 minutes in the hot milk.
In a large saucepan, melt 6 tbsp of butter over medium heat. Just as it begins to sizzle, add the ½ cup of the white flour. Whisk the flour into the butter until completely dissolved. Continue whisking for another couple of minutes to cook the flour, until slightly golden.
Strain the hot milk to discard the bay leaf, onion, and any stray particles. Add the milk to the roux, 1-2 cups at a time, whisking vigorously after each addition. Ensure there are no lumps after all the milk has been incorporated.
Allow the béchamel sauce to heat until gently bubbling, then reduce heat to low. The sauce should thicken and coat the back of a wooden spoon. Add the paprika, mustard, cayenne, Everyday Gourmet, and freshly grated nutmeg and Worcestershire sauce and stir to incorporate.
Drain noodles and rinse in cold water to stop the cooking process and remove the starchy water.
Remove béchamel sauce from the heat and stir in cheeses (reserving some to layer the middle and sides of casserole). Stir cooked macaroni noodles into until well coated and transfer half of mixture to the buttered casserole dish. Place a layer of reserved cheese. Add remaining noodles, and top with remaining reserved cheese and panko breadcrumb topping if using.
Bake on 350 for approximately 30-40 minutes until it is bubbly and golden brown. Remove carefully from the oven and allow to cool for a few minutes before serving.