Cook the pasta: Bring a large pot of salted water to a boil. Add the pasta and cook about 1 minute less than the package directions. Reserve 1 cup of the pasta water, then drain the rest.
Cook the bacon: While the pasta cooks, heat a large saucepan over medium-high heat and add a little oil. Add the diced bacon and cook slowly until golden brown and cooked through (about 4–5 minutes). Remove the bacon and set aside, leaving the rendered fat in the pan.
Cook garlic & shallot: Lower the heat to medium. Add the minced garlic and diced shallot to the pan and cook for 2 minutes, until lightly golden and fragrant.
Add cream: Pour in the cream and ½ cup of the reserved pasta water. Stir and cook for 2 minutes until warmed through.
Add remaining pasta water (if needed): Pour in the remaining ½ cup pasta water. If your sauce is too thin, simmer gently for 2–3 minutes to thicken.
Add cheese: Stir in the grated Pecorino Romano or Parmesan until melted and fully incorporated.
Combine pasta and sauce: Add the drained pasta to the pan and gently toss to coat with the creamy sauce.
Add bacon: Stir the cooked bacon through the pasta and sauce.
Season and serve: Finish with freshly ground black pepper and extra cheese, if desired. Garnish with fresh parsley for a pop of color. Serve immediately.