Place sliced onions, carrots, potatoes, and celery in bottom of the crock-pot.
Put in the rinsed beef brisket, fat side up. Add the juices and sprinkle with the spices from the seasoning packet.
Pour ale over all.
Sprinkle with pepper and add the bay leaf and rosemary.
Cover and cook on low 10-12 hours (or on high 5-6 hours), until beef and vegetables are done. During the last hour or two add the cabbage wedges. Please note that cook times may vary with different crock-pot models.
Remove brisket to cutting board and let rest 10 minutes before slicing. Always slice across the grain.
Serve corned beef and vegetables with horseradish & mustard on the side, with some thick slices of warm Irish Soda Bread slathered in real Irish butter!