Bring a large pot of water to a boil, adding a generous amount of salt. Cook spaghetti al dente, as directed on the package. Then drain and set aside (reserve some of the pasta water if needed)
In a separate large skillet, heat butter over medium heat, adding in the onion and cook for about 2 minutes.
Add the garlic, and cook until fragrant (about 1 minute). Add the chicken broth, lemon juice, lemon zest, cream, salt, and pepper. Cook until it starts to simmer, then add shrimp to the skillet and cook until heated through and pink (about 5 minutes).
Stir in basil and parmesan, then toss the cooked spaghetti with the sauce. Add in 1-2 Tablespoons of reserved pasta water, if needed. Serve immediately topped with a sprinkle of pepper flakes if desired.
Notes
Any type of pasta will do! We love it with angel hair, fettuccine, and penne.