In a large skillet over medium-high heat, add 1 lb of ground beef and cook until browned, about 5-7 minutes. Use a spatula to break the meat into crumbles as it cooks, and drain any excess fat.

Add 1 diced onion and 2 minced garlic cloves to the skillet with the beef. Sauté for about 2-3 minutes until the onion is translucent.

Stir in 1 can of tomato sauce, 1 can of diced tomatoes, 1 teaspoon of Italian seasoning, plus salt and pepper to taste. Simmer for 5 minutes on low heat.

Bring a pot of salted water to a boil. Add elbow macaroni and cook until al dente, about 7-8 minutes. Drain and set aside.

In a large mixing bowl, combine the cooked macaroni with the beef and sauce mixture. Add in 1 cup each of shredded cheddar and mozzarella cheese, and 1/2 cup of sour cream.

Preheat oven to 350°F (175°C). In a greased baking dish, spread half of the macaroni mixture on the bottom. Layer with shredded cheese, then add the remaining macaroni mixture and finish with more cheese.

Cover with foil and bake for 20 minutes, then remove foil and bake for an additional 10-15 minutes until cheese is bubbly and golden brown.

Let the casserole rest for about 5 minutes before serving to allow flavors to settle.