Step 1: Bring a large pot of salted water to a boil. Cook the spaghetti until al dente, about 9–11 minutes according to package instructions. Drain and set aside.

Step 2: Heat olive oil in a large skillet over medium-high heat. Add ground beef and Italian sausage, breaking them up as they cook. Brown thoroughly, then drain any excess grease.

Step 3: Stir in the chopped onion and cook for about 5 minutes until softened. Add minced garlic and cook for 1 more minute until fragrant. Toss in the thawed and squeezed spinach and cook until heated through, about 2–3 minutes.

Step 4: In a separate saucepan, melt butter over medium heat. Whisk in flour and cook for 1 minute to form a roux. Gradually pour in milk and chicken broth while whisking constantly to avoid lumps. Let the sauce simmer and thicken for about 5–7 minutes.

Step 5: Lower heat and stir in heavy cream, Parmesan, mozzarella, Cajun seasoning, Italian seasoning, and smoked paprika. Season with salt and pepper. Stir until cheeses melt and the sauce is smooth and creamy.

Step 6: Add the cooked spaghetti and meat-spinach mixture to the sauce. Toss gently to coat everything evenly in the rich garlic butter sauce.