• Preheat oven to 425°F. Lightly grease a 13x9-inch baking pan with nonstick spray. Set aside.
• Put a large pot of water on the stove top and heat on medium-low while preparing the sauce.

To prepare the sauce:

• Cook the sausage in a large skillet over medium-high heat until browned, breaking up chunks with a spoon. Remove the sausage and any liquid from the skillet. Drain well. Set aside. (Do not wipe out the skillet.)
• Pour the olive oil into the now empty skillet. Add the mushrooms and ¼ teaspoon salt and cook, undisturbed until dark browned. Stir and continue cooking until the mushrooms release their moisture and it evaporates. Reduce the heat to medium. Add the minced shallot. Cook and stir constantly until the shallot softens, about 3 to 4 minutes. Stir in the garlic and red pepper flakes and cook, stirring constantly until fragrant, about 1 minute.
• Carefully pour in the wine. Deglaze the pan by scraping up any crusty bits on the bottom. Add the spinach and cook stirring constantly to wilt. This can be done in two batches if needed. Add the marinara sauce and cooked sausage. Stir to combine then remove from the heat. Cover and set aside while preparing the pasta.

To prepare the pasta:

• Bring the pot of water to a boil over high heat. Cook the manicotti according to package directions, about 7 minutes. Rinse with cold water and drain well.
• In a medium bowl mix together the ricotta, eggs, parsley, salt, pepper and half the Parmesan cheese.
• Spread 3 cups of the meat sauce in the prepared pan. Spoon or pipe the ricotta mixture into the cooked manicotti shells filling each with about ¼ cup. Place the stuffed manicotti in two tight rows or a single layer on top of the sauce in the prepared pan. Repeat until all pasta is filled. Top with remaining sauce. You may have 1 or 2 extra manicotti shells. Refrigerate and use with leftovers or tuck into the casserole if desired.
• Cover the pan with foil and bake for 25 minutes or until the casserole is hot and bubbling. Remove the foil and sprinkle with mozzarella and remaining Parmesan. Bake uncovered until the cheese melts, about 5 to 10 minutes more. Cool 15 minutes then serve garnished with fresh basil, if desired.