Bring a large pot of salted water to a boil. Cook the pasta until al dente, according to package instructions. Reserve 1/2 cup of the starchy pasta water and drain the pasta. Pour the pasta back into the pot.

While the pasta is cooking, heat the olive oil over medium heat in a large skillet. Add the spinach and shallot and cook until spinach is wilted. Add the garlic and cook for 1 minute.

Reduce the heat to low and stir in the ricotta cheese. Add the lemon zest and lemon juice and stir until creamy. Add the reserved pasta water and stir again until well combined. Stir in the Parmesan cheese. Season with salt and black pepper.

Add in the pasta and stir well until pasta is well coated in the ricotta sauce. Garnish with basil, crushed red pepper flakes, and extra Parmesan cheese, if desired. You can also add an extra squeeze of lemon juice if you want a stronger lemon flavor. Serve immediately.