Preheat oven to 350°F. Grease a 13x9-inch baking dish.
Cook macaroni according to package directions until just al dente.
In a medium saucepan, melt butter over medium heat. Gradually whisk in salt, pepper, and flour. Continuously whisk until smooth.
Slowly add milk and bring to a boil. Reduce heat to a simmer and whisk until sauce begins to thicken.
Add buffalo sauce and stir to combine.
Stir in cheddar and Parmesan cheese. Mix until cheese is completely melted, 1-2 minutes.
Add macaroni and chicken to baking dish. Pour sauce over macaroni and stir to combine all ingredients.
Stir together melted butter and breadcrumbs. Sprinkle evenly over macaroni.
Bake uncovered for 30-35 minutes, or until topping is golden brown.