Prepare Creamy Noodle Mixture: In a mixing bowl, whisk together the sour cream, softened cream cheese, cornstarch, and 1/2 cup of the reserved noodle water until the mixture is smooth and well combined.
Combine Noodles and Cream: Stir the cooked egg noodles and the remaining reserved noodle water into the cream cheese mixture. Pour this noodle mixture into a greased 9″x13″ deep-sided baking dish. Spread it evenly and sprinkle with a pinch of salt and pepper.
Layer Beef and Cheese: Top the noodle mixture evenly with the beef mixture, using the back of a spoon to level it out and ensure each noodle is covered. Sprinkle the 2 1/2 cups of Colby Jack cheese generously over the top of the beef layer.
Bake: Bake the Beef Lombardi in the center of the preheated oven for 25-30 minutes, or until the cheese is melted and bubbly and begins to brown slightly on top.
Serve: Remove from the oven and let rest for a few minutes before serving. Enjoy this comforting and cheesy baked pasta dish!
