Bring a large pot of salted water to a boil and cook the spaghetti according to package directions until al dente (usually 8–11 minutes). Before draining, scoop out about ½ cup of the hot pasta water and set aside. Drain pasta and set aside.

While the pasta cooks, heat 2 tbsp olive oil in a large skillet over medium-high heat. Add the chopped onion and cook 3–4 minutes until softened.

Add the ground beef to the skillet and cook 6–8 minutes, breaking it up with a spoon, until browned and no longer pink. Season with salt, pepper, Italian seasoning, and crushed red pepper flakes. Drain excess fat if desired.

Stir in the minced garlic and tomato paste (if using). Cook 30–60 seconds until fragrant.

Pour in the beef or chicken broth and Worcestershire sauce, scraping any browned bits from the bottom of the pan. Let it simmer 2–3 minutes to concentrate the flavors.

Reduce heat to low–medium and stir in the heavy cream, then add the softened cream cheese a few tablespoons at a time, stirring until smooth. Simmer gently for 3–5 minutes until the sauce is creamy and slightly thickened.

Whisk in the grated Parmesan and shredded mozzarella (or cheddar mix). Stir until the cheeses melt into a velvety sauce. If the sauce becomes too thick, add up to ½ cup reserved pasta water, a splash at a time, until you reach your desired consistency. Simmer 2–3 more minutes.

Add the cooked spaghetti directly into the skillet and toss to coat thoroughly. Taste and adjust salt, pepper, or a pinch of lemon zest to brighten the flavors.

Serve immediately, topped with chopped parsley or green onions and an extra sprinkle of Parmesan.