1. Preheat Oven & Cook Pasta:
* Preheat your oven to 375°F (190°C). Lightly grease your 9×13 inch baking dish with cooking spray or olive oil.
* Bring a large pot of generously salted water to a rolling boil. Add the penne pasta and cook according to package directions until it is very al dente – typically 2-3 minutes less than the package recommends. The pasta will continue to cook in the oven, so undercooking slightly at this stage is crucial to prevent it from becoming mushy in the final bake.
* Drain the pasta well in a colander. Do not rinse the pasta (the starch helps the sauce cling). You can toss it with a tiny drizzle of olive oil to prevent sticking if it will sit for a few minutes while you prepare other components.

2. Prepare the Sauce:
* If using Jarred Sauce with Optional Meat/Aromatics: Heat 1 tbsp olive oil in a large skillet over medium-high heat. If using onion, sauté until softened (3-4 mins). Add garlic and cook until fragrant (1 min). Add ground meat (if using) and cook, breaking it up, until browned. Drain off excess fat thoroughly. Stir in the jarred marinara sauce, Italian seasoning, and red pepper flakes (if using). Bring to a simmer, then reduce heat and let it simmer gently for 5-10 minutes for flavors to meld.
* If using Jarred Sauce (Simplest Method): Simply have your jar open and ready. You can warm it slightly in a saucepan if desired, but it’s not essential as it will heat through in the oven.
* If Making Simple Homemade Sauce: Heat 2 tbsp olive oil in a skillet or pot over medium heat. Add onion and sauté until softened (4-5 mins). Add garlic and cook until fragrant (1 min). (If using meat, brown it here and drain fat). Stir in tomato paste (if using) and cook for 1 minute. Add crushed tomatoes, dried herbs, salt, pepper, sugar (if using), and red pepper flakes (if using). Bring to a simmer, then reduce heat, cover partially, and let simmer for at least 15-20 minutes for flavors to develop.

3. Prepare the Ricotta Mixture:
* In a medium bowl, combine the whole milk ricotta cheese, large egg, ½ cup grated Parmesan cheese, finely chopped fresh parsley, ¼ tsp salt, ¼ tsp black pepper, and optional pinch of nutmeg.
* Stir together gently but thoroughly until everything is well combined. Be careful not to overmix vigorously, just ensure no large streaks of egg remain.

4. Assemble the Pasta Bake:
* Method 1: Layered (Classic Style)
* Spread about 1 cup of your prepared sauce evenly over the bottom of the greased 9×13 inch baking dish. This prevents the pasta from sticking.
* Top with about half of the cooked al dente penne pasta, spreading it in an even layer.
* Dollop half of the ricotta mixture evenly over the pasta layer. Use small spoonfuls scattered across the surface.
* Spoon about 1 to 1.5 cups of sauce over the ricotta and pasta.
* Sprinkle with about half (1 cup) of the shredded mozzarella cheese.
* Repeat the layers: remaining pasta, remaining ricotta mixture dolloped evenly, remaining sauce (ensure pasta is well covered).
* Method 2: Mixed (Quicker Assembly)
* In a very large bowl (or directly in the pasta pot if it’s large enough), combine the cooked al dente pasta with most of the prepared sauce (reserve about ½ to 1 cup for the top). Toss gently to coat the pasta evenly.
* Add the prepared ricotta mixture to the pasta and sauce. Gently fold it in – you don’t need it to be perfectly uniform; pockets of ricotta are desirable.
* Pour the pasta mixture into the prepared baking dish and spread evenly.
* Top with the reserved sauce, spreading it lightly over the surface.
* Sprinkle evenly with 1 cup of the shredded mozzarella.

5. Add the Final Cheesy Topping:
* Regardless of the assembly method used, sprinkle the remaining 1 cup of shredded mozzarella cheese evenly over the top of the casserole.
* Sprinkle the final ¼ cup of grated Parmesan cheese over the mozzarella. This adds flavor and helps achieve a beautifully golden-brown crust.

6. Bake the Casserole:
* Carefully place the baking dish into the preheated 375°F (190°C) oven.
* Bake for 25-35 minutes. The casserole is done when the sauce is bubbling around the edges, the cheese topping is fully melted, bubbly, and lightly golden brown in spots. If the top starts browning too quickly before the center is hot, you can loosely tent the dish with aluminum foil for the last 10 minutes of baking.

7. Rest Before Serving (Crucial Step!):
* Remove the pasta bake from the oven and place it on a wire rack. Let it rest for at least 10-15 minutes before cutting and serving. This allows the molten cheese and sauce to set slightly, making it much easier to serve neat portions and preventing burns from super hot filling.