1. Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish and set aside.
2. Cook the spaghetti according to package instructions until al dente. Drain and set aside.
3. In a large skillet over medium heat, heat the olive oil. Add the ground beef and cook until browned, about 6-8 minutes, breaking it up with a spoon as it cooks.
4. Add the diced onion and minced garlic to the skillet and cook for another 3-4 minutes until the onion is soft and translucent.
5. Stir in the Italian seasoning, red pepper flakes (if using), and marinara sauce. Let the mixture simmer for 5 minutes.
6. Reduce the heat and stir in the heavy cream, mixing well to combine. Cook for another 2 minutes until the sauce is heated through.
7. In a large mixing bowl, combine the cooked spaghetti with the sauce, ensuring the pasta is well coated.
8. Transfer half of the spaghetti mixture into the prepared baking dish. Sprinkle with half of the mozzarella and Parmesan cheeses.
9. Add the remaining spaghetti mixture on top and sprinkle with the remaining cheeses.
10. Bake in the preheated oven for 20-25 minutes, or until the cheese is melted and bubbly. Let it rest for a few minutes before serving.

My grandmother always taught me to taste as I go—so don’t be shy to adjust the seasoning to your liking. Her intuitive cooking style is something I cherish and encourage in my own kitchen adventures.