1. Heat the olive oil in a large skillet or Dutch oven over medium heat. Add the chopped onion and cook for about 3 minutes until translucent and fragrant.
2. Add the minced garlic and cook for another 30 seconds, stirring constantly to avoid burning.
3. Toss in the ground beef, breaking it apart with a wooden spoon. Cook until browned and no longer pink, about 6-8 minutes. Drain any excess fat if necessary.
4. Sprinkle in the dried Italian seasoning, salt, and pepper. Stir to combine all the flavors.
5. Pour in the beef broth and bring the mixture to a gentle boil.
6. Add the dry pasta shells directly to the skillet, stirring to submerge them evenly in the broth. Reduce heat to medium-low, cover, and let simmer for 10-12 minutes, stirring occasionally to prevent sticking. The pasta should be tender but still hold its shape.
7. If using spinach or peas, stir them in during the last 3 minutes of cooking to wilt or thaw them.
8. Lower the heat and stir in the milk, shredded cheese, and sour cream. Mix until the cheese melts and the sauce becomes creamy and smooth, about 2-3 minutes. Adjust salt and pepper to taste.
9. Remove from heat and let it sit covered for a couple of minutes to thicken up before serving.

Pro tip from my kitchen: don’t rush the simmering step. Letting the pasta soak up the broth slowly is what gives this dish that comforting, creamy texture that reminds me of my dad’s slow-cooked meals.