01 - Bring a large pot of salted water to a boil over high heat.
02 - Heat olive oil and butter in a large skillet over medium heat. Add chopped onion and sauté until translucent, approximately 3 minutes. Stir in minced garlic and cook for 1 minute until fragrant.
03 - Add fresh spinach to the skillet and cook until just wilted, about 2 minutes. Season lightly with salt and pepper.
04 - Pour heavy cream into the skillet and bring to a gentle simmer. Incorporate half the crumbled feta and all Parmesan cheese, stirring until mostly melted and sauce is smooth. Add nutmeg if using. Reduce heat to low to maintain temperature.
05 - Add gnocchi to boiling water and cook according to package directions until they float to the surface, typically 2–3 minutes. Drain thoroughly in a colander.
06 - Transfer cooked gnocchi to the skillet with the creamy spinach sauce. Toss gently to coat evenly and cook for 1–2 minutes, allowing flavors to meld together.
07 - Remove from heat immediately. Top with remaining crumbled feta and additional black pepper. Serve while warm.