Bring a large pot of salted water to a rolling boil and add the medium pasta shells. Cook according to package instructions, usually around 8–10 minutes, until they are al dente. Drain the shells and set them aside.

In a large skillet, heat over medium heat and add the ground beef. Cook for about 6–8 minutes until browned. Drain excess grease.

Add the chopped onion and minced garlic to the skillet. Sauté for 3–4 minutes until the onion is translucent and the garlic is fragrant.

Sprinkle in the Italian seasoning and pour in the tomato sauce. Stir and bring to a gentle simmer for about 5 minutes.

Reduce heat to low and slowly pour in the cream or milk, stirring continuously, and cook for an additional 2–3 minutes.

Add the cooked pasta shells to the skillet and gently fold them into the creamy beef sauce, stirring for about 2 minutes.

Sprinkle the grated cheddar cheese on top and allow it to melt for about 2–3 minutes.