Trim fat from the meat. In a large skillet, brown the lamb in hot oil over medium-high heat. Drain off the fat.
In the insert of a slow cooker, combine the browned lamb, broth, mushrooms, onions, mustard, garlic, bay leaf, salt and pepper. Cover and cook on low-heat setting for 6 to 8 hours or on high-heat setting for 3 to 4 hours.
In a medium bowl, whisk together the sour cream, flour and sherry until smooth. Sir about 1/2 cup of the hot liquid into the sour cream mixture. Return all to the slow cooker; stir to combine.
Cover and cook on high-heat setting for 30 minutes or until thickened and bubbly. Remove and discard bay leaf. Stir in parsley. Serve over hot noodles.