LOAD CROCK POT: Add 1 ½ pounds chuck roast, trimmed and cut into 1 to 1 ½-inch cubes to a 6-quart slow cooker. Sprinkle with 1 teaspoon kosher salt and ½ teaspoon fresh ground black pepper.
ADD LIQUID AND VEGETABLES: Pour in 1 ¼ cups beef stock. Add 6 ounces coarsely chopped white mushrooms, 1 medium yellow onion, chopped, 3 tablespoons Worcestershire sauce, 1 tablespoon Dijon mustard, heaping, 2 cloves garlic, minced, 1 teaspoon dried parsley, and ½ teaspoon dried thyme. Stir gently to combine.
COOK: Cover and cook on LOW for 8 to 9 hours or HIGH for 4 to 5 hours, until the beef is fork-tender and easily shreds.
COOK NOODLES: About 20 minutes before serving, cook 12 ounces egg noodles according to package directions. Drain well.
FINISH: Stir the cooked noodles and 1 cup sour cream into the slow cooker. Cook on LOW for another 10 to 15 minutes, stirring occasionally, until creamy and heated through.
SERVE: Serve hot.
