Corned beef seems to be more popular in the United States than it is in its native England and Ireland. The meat was originally cured with pellets of salt the size of corn kernels—hence the name “corned beef ” (it’s now cured in brine). Corned beef is usually sold with a ready-made spice packet—or make your own: Add 1 teaspoon whole black peppercorns, ½ teaspoon mustard seed, ¼ teaspoon celery seed, 1 bay leaf, and a pinch of dried crushed red pepper to the cooking liquid.
Rinse brisket and place it in a large Dutch oven. Sprinkle meat with spices (see above). Add water to cover. Bring to a boil; then cover, reduce heat, and simmer 2-½ hours, or until meat is fork-tender. Transfer brisket to a serving platter and keep warm until ready to serve.
Add cabbage and carrots to cooking liquid; cover and cook 15 minutes, or until vegetables are crisp-tender. Add peas and cook 5 minutes longer.
Slice brisket thinly, diagonally across the grain of the meat. Discard bay leaf and arrange vegetables around brisket. Serve with Horseradish–Chive Sauce or your favorite mustard.
Combine sour cream, horseradish, and chives, stirring ingredient mixture well.
Cover and chill.