Cook pasta according to package directions. Reserve 1 cup of cooking water and drain pasta.
While the pasta is cooking, melt butter in a large skillet over medium-low heat. Add garlic and stir for about a minute, until fragrant. Add spinach and cook until wilted, 5 minutes.
Lower the heat to low and add ricotta, parmesan, lemon juice and zest and stir well. Stir in ½ cup of pasta water until smooth. Add pasta and toss the pasta until well-coated. Add more pasta water as needed.
Notes
Best to eat immediately, but can refrigerate for 3-4 days. The sauce will separate, so when reheating on the stovetop, add a splash of milk or water.