Place beef, garlic, onion, water, soup, bouillon, Worcestershire and dry soup mix in crock pot.
Cook on low for at least 4 hours.
Sauté chopped mushrooms in butter.
Approx ½ to 1 hr before serving stir in the cornstarch, water mixture, cream cheese, sour cream and the mushrooms.
Serve over warm egg noodles.
(I used a combination of beef London broil and ranch steaks, cubed up as that is what I had available. Portabella mushrooms were on sale so I got 6 oz worth and sautéed them before adding them. I had a bit more than 1/3 cup sour cream to use up so I used the minimum amount of cream cheese. On allrecipes.com the reviewers commented that using cream cheese resulted in a meal that reheated better but had less tang than when sour cream was used.)