Bring a large pot of salted water to a boil. Salt generously— the pasta water should taste like the sea. Add the pasta and cook until just shy of al dente (about 1-2 minutes less than package directions).

While the pasta cooks, warm a large skillet over medium heat and add the olive oil. Sauté the garlic for 30-60 seconds until fragrant but not browned.

Add the spinach to the skillet in batches, tossing until wilted (about 1-2 minutes). Season with salt and pepper, and add red pepper flakes if desired. Transfer the spinach to a bowl and set aside.

Reserve ½ cup of the pasta cooking water, then drain the pasta.

In the same skillet (wipe it quickly if needed), off the heat, combine the ricotta, lemon zest, lemon juice, Parmesan, butter (if using), and ¼ cup of the reserved pasta water. Stir until smooth. If it looks too thick, add the remaining reserved water a splash at a time.

Add the drained pasta to the skillet and toss gently with the ricotta sauce until the noodles are evenly coated. Fold in the wilted spinach. Taste and add salt and pepper as needed.

Serve immediately with an extra sprinkle of Parmesan, a twist of lemon, and a light drizzle of olive oil. If adding protein like shredded chicken or shrimp, fold it in at the end to warm through.