• Preheat the oven to 350°F and lightly grease a 9 x 13-inch baking dish.

Prepare the Meat Sauce

• Heat the olive oil in a large skillet over medium heat.
• Add the onion, ½ teaspoon of salt and ¼ teaspoon of black pepper.
• Sauté until softened and translucent, about 4 minutes.
• Stir in the garlic and cook for 30 seconds, until fragrant.
• Add the ground sweet Italian sausage to the skillet.
• Cook, breaking it apart with a spoon, until browned and fully cooked, 6 to 8 minutes.
• Drain any excess grease.
• Stir the marinara sauce into the skillet with the sausage.
• Bring the sauce to a simmer and let it cook for 5 to 7 minutes, stirring occasionally.

Cook the Pasta

• Meanwhile, cook the mostaccioli pasta in salted water according to the package instructions for al dente.
• Drain and set aside.

Assemble the Pasta Bake

• In a medium bowl, mix together the ricotta cheese, egg, ½ cup of grated Parmesan, ½ teaspoon of salt, ¼ teaspoon of black pepper and the crushed red pepper until smooth.
• Toss the cooked pasta with the meat sauce until evenly coated.
• Spread half of the pasta mixture into the prepared baking dish.
• Spread the ricotta mixture evenly over the pasta layer, then top with the remaining pasta and sauce.
• Sprinkle the shredded mozzarella and remaining 3 tablespoons of parmesan cheese over the top.

Bake and Garnish

• Cover the dish with foil and bake for 20 minutes.
• Remove the foil and bake for another 10 minutes, or until the cheese is melted and bubbly.
• Garnish with fresh basil leaves and serve hot.