Bring a big pot of water to a rolling boil. Add 1 teaspoon salt to the water – your pasta will thank you.
Toss in the cellentani pasta and cook it until it's just al dente (check your package, but usually 8-9 minutes). Pro tip: Keep it slightly firmer than you'd normally eat it since it'll continue cooking in the oven.
Drain it well in a colander, give it a little shake to get rid of extra water, and set it aside.
Preheat your oven to 375°F (190°C). Grab a 9×13 baking dish and give it a quick coat of cooking spray.
Heat up a large, deep skillet over medium-high heat. Add your ground beef and chopped onion, breaking the meat apart as it cooks.
While the meat browns, sprinkle in the salt, pepper, paprika, Italian seasoning, and red pepper flakes.
Cook until you don't see any pink in the beef and the onions look soft and translucent, about 5-7 minutes.
Carefully drain off the extra grease, but leave just enough to keep everything moist.
Lower the heat to medium-low and add the minced garlic. Stir it constantly for about 30 seconds until you can really smell that gorgeous garlic aroma.
Pour in both the marinara and Alfredo sauces, stirring until everything's well combined with the meat.
Let it simmer gently for 2-3 minutes.
Spread the cooked pasta evenly in your prepared baking dish.
Pour the warm, amazing meat sauce over the pasta, and gently fold it all together until every piece of pasta is coated.
Use your spatula to smooth the top so it's nice and even.
Sprinkle the mozzarella cheese over the entire surface – don't leave any spots uncovered!
Place your dish on the middle rack of your preheated oven.
Bake it uncovered for 20-25 minutes, until the cheese completely melts and starts to get brown and bubbly around the edges.
Optional: Switch to broil for the final 1-2 minutes, but watch it closely.
Pull it out and immediately sprinkle with Parmesan cheese and dried parsley while it's still hot.
Let it rest for 5 minutes before serving.
