1. The night before you will make your stew, put the brisket or corned beef in your slow-cooker.
2. Cover with beef broth and any additional water needed to cover the meat. Cook on low until morning.
3. Remove beef and set aside to cool.
4. Peel and cut the onions into 1 inch chunks. Peel and cut the carrots into 1 inch slices. Cut the celery into 1 inch slices. Cut the potatoes into 2 inch pieces.
5. In a heavy bottom pot, heat the oil and add the onion, salt, and pepper.
6. Once the onion has become tender and fragrant, add the garlic, carrots, celery, potatoes, and thyme. Stir occasionally for 10 minutes.
7. Add the cooking liquid from your slow-cooker and the bay leaf. Bring stock to a boil and turn down to a simmer. Simmer for an hour or until all veggies are tender.
8. Chop corned beef or brisket into 2 inch pieces and add to stew. Cook for another 15 minutes.
9. While beef cooks, chop parsley. Sprinkle with chopped fresh parsley before serving.