Bring a large pot of salted water to a boil and cook the pasta shells according to package directions until al dente (usually 8–10 minutes). Drain and set aside.

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

Add the minced garlic and cook for 30 seconds until fragrant.

Add 1 lb ground beef to the skillet. Break it apart with a spatula and cook for 6–8 minutes until browned and no pink remains. Drain any excess fat if needed.

Stir in 1 tbsp tomato paste (if using), Italian seasoning, smoked paprika, salt, and pepper. Cook for 1 minute to bloom the spices.

Pour in 1 cup beef broth and bring to a simmer. Let it reduce for 3–5 minutes so the flavors concentrate.

Lower heat to medium-low and add 1 cup heavy cream and 1/2 cup milk. Stir to combine and simmer gently for 4–6 minutes until the sauce thickens slightly.

Stir in 1 cup shredded cheddar and 1/2 cup Parmesan until melted and smooth. Taste and adjust seasoning.

Add the drained pasta shells to the skillet (or combine in a large mixing bowl if your skillet is small). Toss gently so every shell gets coated in the creamy beef sauce.

If the sauce seems too thick, stir in a splash of pasta water or extra milk.

Garnish with chopped parsley and a sprinkle of red pepper flakes if desired. Serve immediately.