Start by bringing a large pot of salted water to a boil. Carefully add the 9 lasagna noodles and cook according to package directions until al dente—usually about 8 to 10 minutes. Drain and lay them flat on a clean kitchen towel or parchment paper to prevent sticking.
Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the chopped onion and cook until soft and translucent, about 5 minutes. Stir in the minced garlic and cook for another minute until fragrant. Add the chopped spinach in batches, stirring until wilted and any excess moisture evaporates. Remove from heat and set aside.
In a medium saucepan, pour in the 2 cups of heavy cream and warm over medium heat. Whisk in the Italian seasoning, salt, and pepper. Slowly add the grated Parmesan cheese, whisking continuously until the sauce thickens and becomes smooth. Remove from heat once it reaches a creamy consistency.
In a mixing bowl, combine the ricotta cheese with half of the sautéed spinach mixture. Season with a pinch of salt and pepper, stirring gently to blend.
Preheat your oven to 375°F (190°C). Spread a thin layer of Alfredo sauce on the bottom of your baking dish. Lay down three lasagna noodles side by side. Spread half of the ricotta-spinach mixture over the noodles, followed by a generous layer of Alfredo sauce. Sprinkle a third of the shredded mozzarella cheese on top.
Add another layer of three noodles, then the remaining ricotta-spinach mixture, more Alfredo sauce, and another third of mozzarella. Finish with the last three noodles, the remaining Alfredo sauce, sautéed spinach (reserved), and the final third of mozzarella cheese.
Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15 minutes or until the top is golden and bubbly. Let the lasagna rest for 10 minutes before slicing to allow the layers to set beautifully.
