Cook the chopped pancetta until crispy and set aside, reserving the fat
Cook the medium pasta shells according to package directions and drain
In a large pot, melt pancetta fat and butter together
Whisk in all-purpose flour to create a roux
Gradually add warmed half & half, stirring constantly to avoid lumps
Stir in grated garlic and Dijon mustard
Season with kosher salt, black pepper, and a pinch of nutmeg to taste
Remove from heat and fold in the shredded white cheddar, Monterey Jack, Gruyère, and Parmesan until melted and smooth
Fold in the cooked pasta shells and crispy pancetta
Transfer to a serving dish and top with additional Parmesan and fresh chives
