1 ½ pounds beef stew meat
8 ounces mushrooms, quartered
6 cups beef broth
2 tablespoons Worcestershire sauce
2 teaspoons onion powder
2 teaspoons garlic powder
2 teaspoons salt
½ teaspoon freshly ground black pepper
½ cup sour cream
1/3 cup cold water
1/4 cup cornstarch
8 ounces egg noodles, cooked according to package directions
In the slow cooker, stir together the meat, mushrooms, broth, Worcestershire sauce, onion powder, garlic powder, salt, and pepper. Cover and cook for 6 hours on low.
In a glass measuring cup, combine the sour cream with 1 cup of the liquid from the slow cooker, and stir it until it's well combined and smooth. Stir the mixture back into the pot. In a small bowl, whisk the water and cornstarch together until well combined, and then add it to the slow cooker.
Cover and cook for 1 more hour on high. Just before serving, stir in the noodles. Serve hot.