Preheat oven to 375°F. Cook pasta according to package until al dente; drain and set aside.
Cook pancetta in a large oven-safe skillet over medium about 6-8 minutes until crispy; remove and set aside.
Melt butter in same skillet; whisk in flour and cook 1-2 minutes.
Gradually whisk in warm milk and cream constantly about 5 minutes until thickened.
Remove from heat; stir in Gruyère and fontina until completely melted and smooth. Season with salt and pepper.
Stir in pasta and half the pancetta.
Mix panko and Parmesan; sprinkle over top, then add remaining pancetta.
Bake 15-20 minutes until golden and bubbly; drizzle with truffle oil and garnish with parsley before serving.