Bring a large pot of salted water to boil. Add pasta and cook for time per packet MINUS 2 minutes (finishes cooking in Sauce).
SCOOP OUT a mugful of pasta cooking water, then drain.
Meanwhile, cook bacon until golden, drain on paper towels.
Season chicken on both sides, cook in bacon fat, 2 minutes each side.
Wipe pan - optional, to keep sauce pretty and white, and for a buttery clean tasting sauce rather than very bacony (Note 3).
Over medium heat, melt butter. Add garlic and onion, cook for 3 - 4 minutes until onion is light golden and soft.
Add cream, about ¾ cup pasta water and parmesan. Stir, then simmer for 2 minutes until it reduces slightly - you don’t need to be exact here. Season with salt & pepper.
Add pasta and toss gently in the sauce for about 1 ½ minutes. The sauce will thicken and coat the pasta, do this step until you get the sauce consistency you want. If your sauce gets too thick, add a splash of pasta water.
Toss through bacon and chicken.
Serve immediately, garnished with parmesan and parsley!