Instructions:
- Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
- Boil ziti according to package directions until al dente (about 1 minute less than suggested). Drain well and set aside.
- Heat olive oil in a large skillet over medium heat. Sauté onion until soft and translucent (about 5 minutes). Add garlic, Italian seasoning, and red pepper flakes; cook until fragrant (about 1 minute).
- Pour in crushed tomatoes and broth. Season with salt, pepper, and sugar. Bring to a simmer, then reduce heat and cook gently for 10 minutes.
- Stir the fresh spinach into the simmering sauce in batches until completely wilted down (about 3 minutes). Remove sauce from heat.
- In a large mixing bowl, combine the ricotta, Parmesan, beaten egg, basil, nutmeg, salt, and pepper. Stir until evenly mixed. Fold in 3 oz of the shredded mozzarella.
- Add the cooked, drained pasta directly into the skillet with the tomato-spinach sauce. Stir gently to coat all the pasta.
- Assemble layers: Spread half of the sauced pasta mixture into the prepared baking dish. Dollop spoonfuls of the ricotta mixture evenly over the pasta layer. Top with the remaining sauced pasta mixture.
- Sprinkle the remaining 1 cup of shredded mozzarella and a light dusting of extra Parmesan over the top layer.
- Bake for 25–30 minutes, or until bubbly around the edges. Broil for the last 2–3 minutes for a golden crust.
- Let the dish rest for 10 minutes before slicing and serving.