In the same skillet over high heat, brown the carrots, celery, mushrooms and onion, adding oil as needed. Season with salt and pepper. Add the garlic and mustard and cook for about 2 minutes. Deglaze with the wine and add the broth. Bring to a boil and pour into the slow cooker. Cook until the meat is fork-tender, about 5 hours on the low setting or 3 hours on high. Sprinkle with parsley. Adjust the seasoning.
