In a mixing bowl, combine the 1 diced large white onion, 1 cup sour cream, and 1 package (3 oz.) cream cheese. Stir until the mixture is smooth and evenly blended.
Assemble Casserole: Layer half of the cooked egg noodles in the bottom of the prepared casserole dish. Top this with half of the sour cream mixture, spreading it out evenly. Follow with half of the beef and tomato sauce mixture, spreading it over the creamy layer. Repeat these layers: add the remaining noodles, then the rest of the sour cream mixture, and finally the remaining beef mixture. Sprinkle the top generously with ½ cup shredded sharp Cheddar cheese (or more, to your liking).Bake: Place the casserole in the preheated oven. Bake for about 25 minutes, or until the cheese is completely melted and the casserole is bubbly and heated through.Serve: Remove from the oven, let it cool for a few minutes, and then serve warm. Enjoy!
