Transfer liquid from pot roast into Dutch oven. Add mushrooms, onions, wine and marjoram leaves to liquid in pan.
Bring to a boil, reduce heat and simmer, uncovered, 7-8 minutes until vegetables are almost tender; stir occasionally.
Cut pot roast into 1-inch pieces; add to pan. Bring to a boil; cook 2-3 minutes until beef is heated through.
Stir in cornstarch. Bring to a boil; cook and stir until thickened.
Serve over prepared noodles.
Other ways to serve fully cooked pot roast. Add to ready-to-eat rice and pasta combinations for a hearty casserole; Jazz up a bean burrito; Take a roast beef sandwich "up-a-notch" by adding fried onion rings and jalapeno catsup; Chop or shred and add to potato, onion or tortilla soup.
