Place enamel cast iron Dutchoven on top of burner. Turn burner on to medium heat. Heat pan just a little;add 1 Tblsp oil. When oil is hot, add chopped onion, and cook, stirring for 2minutes. Add mushrooms and cook for 2 more minutes. Remove from pan.
Add 1 Tblsp oil and heat.Dredge beef in flour. Add half of beef to Dutch oven, making sure there is only a single layer of beef. If you put all the beef in and it lays on top of each other, the meat will steam rather than saute. Saute till just brown; remove. If needed, add more oil to the pan and cook the second batch of beef. Remove.
Add water, Worcestershire sauce, and beef base to Dutch oven. Stir until the beef base is dissolved and all the stuck particles on the bottom of the pan come loose. Add beef, onions, and mushrooms; stir. Turn off heat, put on the lid, and put entire Dutch oven into a 325 degree oven.
Cook for 1 hour. Remove fromoven, place on stove burner and return heat to medium. Stir 1 Tblsp flour into¼ cup water; stir into stroganoff and continue stirring until liquid thickens.Turn off heat and add ¼ cup sour cream, stirring until smooth.
Serve over hot egg noodles or mashed potatoes.