In a large heavy skillet, heat the oil over medium high heat. Add the meat and onion - sauté until the meat is browned and the onion is softened. Reduce the heat to low. Stir in the water, beef broth, Worcestershire sauce, & mushrooms. Cover the skillet and simmer until the meat is fall apart tender, about 45 minutes.
Push the meat to one side of the skillet and whisk in the gravy mix. Sprinkle with the flour and stir it to mix. Simmer until thickened, about 1 minute. Keep warm over very low heat.
Meanwhile in a large pot of boiling water, cook the noodles until tender - about 5 minutes. Drain the noodles.
Stir the sour cream and salt into the meat mixture. Gently heat through, stirring, but do not let the mixture even simmer or the sour cream will separate. Spoon over the cooked noodles and serve immediately. Alternatively, you can mix the meat and sauce in with the noodles instead of serving the meat over top.
