Add the strips of bacon to a large sauté pan and heat over medium heat. Cook the bacon until the fat is rendered and the bacon is crispy, about 5 minutes.
Use a slotted spoon to remove the bacon, reserving as much fat in the pan as possible, about ¼ cup.
Return the pan to medium heat, add the butter and allow to melt. Add the onion and sauté, stirring occasionally, until the onion is soft and opaque, about 5 minutes. Add the garlic and red pepper flakes and cook for an additional 30 seconds.
Add the tomatoes, stirring to combine. Let cook until the tomatoes start to break down, about 2 to 3 minutes. Stir in the heavy cream and creme fraiche. Season the sauce with salt and pepper then set aside.
Bring a large pot of water to a boil; add salt and bring back to a boil. Add the pappardelle and cook, stirring occasionally, until al dente, about 8 minutes.
Reserve 1 cup of the pasta cooking water and set aside then drain the noodles and return to the pot. Add the sauce and ½ cup of the pasta cooking water, tossing to coat.
Add the Parmesan and cooked bacon and continue to toss until the noodles are coated and the sauce is glossy.
Divide the pasta among plates and garnish with the chives.