1. Bring a large pot of salted water to a boil. Add the spaghetti and cook until just al dente according to package directions. Reserve ¼ cup pasta water, then drain and set aside.

2. In a large skillet, heat olive oil over medium heat. Add diced onion and sauté for 3–4 minutes until translucent. Stir in garlic and cook for 30 seconds.

3. Add ground beef to the skillet. Season with salt, pepper, and Italian seasoning. Cook until browned, breaking it up with a spoon, about 6–8 minutes. Drain excess fat.

4. Pour in the marinara sauce and crushed red pepper flakes (if using). Stir and reduce heat. Let the sauce simmer for 15–20 minutes to deepen the flavor.

5. Turn off the heat. Add Velveeta cubes and milk to the sauce. Stir until melted and the sauce becomes smooth and creamy. Use reserved pasta water to thin it out if needed.

6. Add the cooked spaghetti to the skillet and toss to coat all the noodles evenly with the sauce. Let sit for a minute before serving.

7. Serve hot, topped with fresh parsley or basil and a sprinkle of Parmesan cheese if desired.