Cook pasta in salted water according to directions for al dente. Remove from heat and drain. Set aside.

Bring small skillet to medium high heat. Add dice pancetta and fry until crisp, remove from heat and drain. Set aside for garnish.
Slice scallions on the diagonal until just in the whites of the green onion. Place in fridge until time to garnish.

Melt the butter in a Dutch oven over medium heat. Add the flour and mustard and stir with a wooden spoon or whisk until a thick paste forms, 2 to 3 minutes.

Stir in the cream and bring mixture to a simmer, stirring until the sauce becomes thick.

Add the Gouda, Gruyere, Asiago, Cheddar, and white Cheddar, stirring the cheeses until melted and the sauce is smooth. Add the cooked pasta and stir well to combine.

Stir in the sour cream, salt, white pepper and cayenne. Cook until the ingredients are combined and hot, 2 to 3 minutes.

Transfer to serving bowl, top with pancetta and scallions.