9 to 12 lasagna noodles (uncooked or no-boil)

15 oz ricotta cheese (whole-milk)

10 oz frozen spinach (thawed and squeezed completely dry) or 4 cups fresh chopped spinach

1 large egg

3 to 3.5 cups marinara or pasta sauce (about one 24- to 28-oz jar)

3 to 4 cups shredded mozzarella cheese (divided)

1 cup grated Parmesan cheese

1 tsp salt and

¼ tsp black pepper

1. Preheat your oven to 375°F (190°C).
   
   
2. Prepare the noodles by boiling them in salted water until al dente, unless you are using no-boil noodles.
   
   
3. Make the filling in a large bowl by mixing the ricotta cheese, squeezed dry spinach, egg, half of the mozzarella, half of the Parmesan, salt, and pepper.
   
   
4. Layer the pan by spreading a thin layer of marinara sauce on the bottom of a 9x13-inch baking dish.
   
   
5. Add a layer of noodles, spread a portion of the spinach-ricotta mixture over them, and top with more sauce.
   
   
6. Repeat the layers until you run out of ingredients, ensuring the final top layer is noodles covered with extra sauce and the remaining mozzarella and Parmesan cheeses.
   
   
7. Bake covered with aluminum foil for 25 minutes.
   
   
8. Remove the foil and bake for another 10 to 15 minutes until the cheese on top is melted and golden brown. 
   
   
9. Cool and serve by letting the lasagna rest for 15 minutes so the slices hold their shape.