Cut up any large pieces of stew meat. In a large skillet, brown meat, half at a time, in hot oil. Drain off fat.
In a 3 ½- or 4-quart slow cooker place browned meat, onions, garlic, oregano, salt, thyme, pepper, and bay leaf. Add beef broth and sherry. Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours. Discard bay leaf.
If using low-heat setting, turn to high-heat setting. In a bowl, whisk together sour cream, flour, and water until smooth. Stir about 1 cup of the hot liquid into sour cream mixture. Return all to cooker; stir to combine. Cover and cook about 30 minutes more or until thickened and bubbly. If desired, serve over hot cooked pasta; sprinkle with parsley.