Make this easy beef dish with leftover rare roast beef, or you can use any beef solid for stir-fry. I found this recipe in Eat Cheap But Eat Well. I have not tried this recipe, but I'm posting it for safe keeping.
Melt 1 tablespoon of butter in a large skillet over medium heat. Add the beef and cook, stirring occasionally, until browned. Stir in the onion soup mix. Add 1/2 cup water and the mushrooms, including their juice. Reduce the heat, cover, and simmer for 5 minutes.
Meanwhile, cook the noodles according to the package directions. When the noodles are done, drain them. Mix the sour cream into the meat mixture and stir until warm. Toss the noodles with the remaining 1 tablespoon butter and the parsley and serve the beef mixture on top.