Preheat your oven to 350 degrees Fahrenheit and spray a 9x13 glass baking dish with nonstick spray. Set aside.
Cook 16 oz mostaccioli according to the box instructions until al dente. You can make the sauce while your pasta is cooking.
To make the sauce, add 2 tbsp olive oil into a large saucepan over medium-high heat.
Once warm, add one yellow diced onion and saute for 5 minutes until the onions begin to turn translucent. Once the onions are sweating, add the ½ tbsp garlic and cook for another minute or so.
Add 1 lb ground beef into the saucepan along with the 1 ½ tbsp Italian seasoning. Cook until the ground beef is cooked all the way through, using a wooden spoon to break up the meat.
Once the beef is cooked, add 36 oz marinara sauce into the saucepan and cook until it just starts to bubble. Then add the 1 ½ cup heavy cream and stir. Cook again until the sauce begins to bubble.
Add the ¾ cup grated parmesan cheese into the sauce and stir once again until the cheese is combined. Taste the sauce and salt to taste.
In a large pot or bowl, toss the cooked pasta with the sauce.
Pour the pasta into the prepared 9x13 pan. Sprinkle the 2 cups shredded mozzarella on top of the pasta.
Put the pasta in the oven and set the timer for 15 minutes. Your Mostaccioli Pasta Bake is done when the cheese is melted and the sauce just begins to bubble. Serve and enjoy!