1 4 to 5 lb piece corned beef brisket, rinsed
2 lbs. small red potatoes, halved
3 carrots, cut into 2-inch pieces
1 large onion, cut into 1/2-inch wedges
2 or 3 sprigs fresh thyme
12 oz. stout beer
2 T. pickling spice
1/2 small head green cabbage, core intact and cut into thick wedges
1/2 cup sour cream
1/4 cup prepared cream horseradish
2 T. whole-grain mustard
3 T. unsalted butter
Salt and pepper to taste
1/2 cup chopped parsley
Layer the potatoes, carrots, onions and thyme in a crock pot. Put the brisket on top of the vegetables and add the beer and pickling spice. Add enough water to just cover the brisket. Cover and cook on low until the meat and vegetables are tender, about 8 hours.
Arrange the cabbage over the brisket, cover and cook until soft and wilted, 45 minutes to 1 hour more.
Whisk together the sour cream, horseradish and mustard in a small bowl.
Removed cabbage and toss with 1 T. of the butter and pepper to taste in a large bowl. Remove the meat and let it rest. Strain the remaining vegetables and toss with the parsley, the remaining 2 T. butter and salt and pepper to taste.
Slice the corned beef against the grain and serve alongside the vegetables and drizzled with the horseradish sauce.