Cook spaghetti according to package directions until al dente. Drain and set aside.

In a skillet, brown ground beef with diced onion over medium heat until fully cooked. Add garlic and sauté for 1 minute.

Stir in tomato sauce, Italian seasoning, salt, and pepper. Simmer for 5–10 minutes.

In a bowl, mix cooked spaghetti with cream cheese and sour cream until evenly coated.

In a greased 9×13-inch baking dish, layer half the creamy spaghetti, half the meat sauce, and a layer of cheddar cheese.

Repeat the layers with remaining ingredients, ending with cheddar cheese on top.

Cover with foil and bake at 350°F for 25 minutes. Uncover and bake an additional 10–15 minutes until bubbly and golden.

Let rest for 5 minutes before serving.