Method:

1. In a large stock pot, add the brisket and enough cold water to cover by 4 inches. Add the bay leaves, thyme, juniper, peppercorns, mustard seed, cloves, onion, and garlic. Set over high heat and bring to a low boil, then lower the heat to maintain a strong simmer. Skim off and discard any scum that rises to the surface. Cook until the meat is fork-tender but not falling apart, about 3 hours. 

2. Add the cabbage, potatoes, turnips, beets, carrots, and parsnips, then return to a simmer and cook until the vegetables are barely tender when poked with a fork, 40–50 minutes. Add the olives and continue cooking 10 minutes more. 

3. Use a slotted spoon or a spider skimmer to transfer the vegetables to a large-rimmed baking sheet or platter, taking care not to break them into pieces. Discard the onion and garlic. Place a colander over a large bowl and drain the meat, saving the cooking liquid for drizzling or for reheating leftovers. Transfer the meat to a cutting board and thinly slice against the grain. Arrange the vegetables around the meat and drizzle with cooking liquid, if desired. Serve hot or cold, with mustard or horseradish on the side.