Make the sauce:
In a large pot, melt the butter over medium heat. Add the minced garlic and cook for 1 minute until fragrant. Stir in the ricotta, salt, pepper, lemon zest, lemon juice, and Parmesan. Whisk everything together until smooth. Gradually add the reserved pasta water, a little at a time, until the sauce reaches a creamy consistency. If you like it extra creamy, feel free to stir in a bit more Parmesan.