Cook the pasta according to the package directions, then drain and set aside.
Preheat the oven to 350°F (177°C).
In a 10-inch skillet, heat the oil over medium-high heat. Add the ground beef, onions, garlic, Italian seasoning, salt, and pepper. Cook, breaking up the beef, until browned and no longer pink, about 4 minutes. Drain any excess grease and transfer to a medium bowl.
Stir in the tomato sauce, sour cream, cooked pasta, and ½ cup shredded cheese until evenly mixed.
Lightly grease a 4x6-inch or 5x5-inch baking dish. Pour in the mixture, sprinkle the remaining 2 tablespoons of cheese on top, and bake for 20–25 minutes, until the cheese is melted and bubbly.
Remove from the oven and enjoy warm.
Notes
Use Lean Ground Beef: Choose 90% lean ground beef for rich flavor without too much grease. If using a higher-fat blend, drain it well before mixing.
Shred Your Own Cheese: Freshly shredded cheese melts smoother and gives your ground beef casserole better texture and flavor than pre-shredded cheese.
Choose the Right Pasta: Penne is a great choice, but rotini, shells, or elbow macaroni also work perfectly in this easy hamburger casserole.
If doubling this recipe, use either two 5x5 inch baking dishes or one 6x8 inch baking dish.