3 ounces mild white cheddar cheese, shredded (about 1 cup shredded)
1 lb shredded sharp cheddar cheese
3 ounces Gruyere cheese, shredded (about 1 cup shredded)
2 ounces Pecorino cheese, finely shredded (about 3/4 cup shredded)
1 ounce (2 slices) yellow American cheese, finely chopped
1/4 cup Panko bread crumbs
Place an oven rack in the top half of the oven. Heat oven to 450.
Bring a large pot of salted water to a rolling boil on the stovetop.
Add macaroni and cook for 5 minutes or until just barely al dente. Strain and set aside.
Heat butter in a 10-inch cast iron skillet or oven-safe saucepan set over medium-high heat. When butter is melted and foamy, sprinkle over flour, whisking to incorporate into a smooth paste. Continue to whisk until frothy and light golden brown, about 2 to 3 minutes. Slowly drizzle in milk, whisking vigorously. If at any point the mixture clumps, continue to whisk until smooth before adding more milk. Continue whisking until all the milk has been added. Cook, whisking regularly, for 7 to 8 minutes or until sauce has thickened to the consistency of heavy cream and just barely starts to simmer around the edges. Whisk in cayenne, paprika, and salt and pepper to taste. Remove from heat.
Set aside 1/4 cup of cheese (a mix of cheddar, gruyere, and pecorino). Slowly add remaining cheese to skillet, one handful at a time, whisking well until melted and smooth. If the sauce still has noticeable chunks in it, return pan to low heat and continue whisking for no more than 1 to 2 minutes or until cheese is completely melted.
Fold cooked macaroni into cheese sauce until evenly coated. Sprinkle with reserved shredded cheese and bread crumbs and broil on high for 4 to 5 minutes or until cheese is bubbly and breadcrumbs are golden brown. Remove from oven and let cool for 5 minutes before serving.