Whisk 1 cup ricotta, 1 Tbsp oil, 1/4 tsp pepper, and 1/8 tsp salt in medium bowl until smooth, set aside.
Bring 4 quts water to boil in large pot. Add pasta and 1 Tbsp salt and cook until al dente. Reserve 1 cup cooking water. Stir spinach into pot with pasta and cook until wilted, about 30 sec. Drain pasta and spinach and return them to pot.
While pasta cooks, heat remaining 2 Tbsp oil, garlic, nutmeg, and cayenne in small saucepan until fragrant, about 1 min. Remove pan from heat and whisk in remaining 1/3 cup ricotta, cream, lemon zest, lemon juice, and 3/4 tsp salt until smooth.
Add ricotta-cream mixture in small saucepan and Parmesan to pasta and toss to combine. Let pasta rest, tossing frequently, until sauce has thickened slightly and coats pasta, 2-4 min, andjust consistency with reserved cooking water as needed. Transfer to plates and dot evenly with reserved ricotta mixture, serve, passing extra Parmesan.