Begin by bringing a large pot of salted water to a boil. Add your chosen short pasta and cook according to package instructions until al dente, usually around 7-10 minutes. Once cooked, drain the pasta and set it aside.

In a large, heavy-bottomed pot over medium heat, melt 4 tablespoons of butter. Once melted, sprinkle in 1/4 cup of all-purpose flour, stirring constantly for 1-2 minutes until the mixture becomes a light golden color.

Gradually whisk in 3 cups of milk into the roux, continuing to stir to prevent lumps. Cook for about 5-7 minutes until the sauce thickens and begins to bubble gently.

Once the milk mixture has thickened, stir in 1/2 cup of buffalo sauce, adjusting for heat preference. Allow to simmer for an additional minute while stirring.

Turn off the heat and mix in 1 cup of shredded mozzarella cheese, 1 cup of shredded cheddar cheese, and 1/2 cup of sour cream. Stir until melted and well incorporated.

Gently fold the drained pasta into the cheese sauce, ensuring every piece is evenly coated.

Transfer the mac and cheese mixture into a lightly greased baking dish. Sprinkle the top with an additional cup of shredded cheese and broil at 400°F for 5-10 minutes until golden.

Once broiled, let it rest for a couple of minutes. Top with chopped chives and crispy onions and serve warm.