Boil the pasta: Bring a large pot of salted water to a boil. Cook pasta until just al dente.
Reserve 1/2 cup pasta water, then drain.
Season the shrimp: Pat shrimp dry. Season with a pinch of salt, pepper, and a little red pepper flakes if using.
Sear the shrimp: Heat olive oil in a large skillet over medium-high. Add shrimp in a single layer and cook 1–2 minutes per side until just pink.
Transfer to a plate.
Build the sauce base: Reduce heat to medium. Add butter to the same skillet. Stir in garlic and cook 30–45 seconds until fragrant, not browned.
Deglaze: Pour in white wine or broth.
Simmer 1–2 minutes, scraping up any browned bits.
Make it creamy: Stir in heavy cream. Simmer gently 2–3 minutes to thicken slightly. Lower heat if it bubbles too hard.
Add cheese and brightness: Whisk in Parmesan until smooth.
Add lemon zest and lemon juice. Taste and season with salt and pepper.
Toss with pasta: Add cooked pasta and a splash of reserved pasta water. Toss until glossy and well-coated.
Finish with shrimp: Return shrimp to the pan.
Toss 30–60 seconds to warm through. Adjust with more lemon, pepper, or pasta water as needed.
Serve: Top with parsley and extra Parmesan. Serve immediately.