Instructions
Step 1
In a large stock pot, add the brisket and enough cold water to cover by 4 inches. Add the juniper, mustard seeds, peppercorns, thyme, cloves, bay leaves, garlic, and onion. 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.
Step 2
Add the potatoes, beets, carrots, parsnips, turnips, and cabbage, 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.
Step 3
Using a slotted spoon or a spider skimmer, transfer the vegetables to a large rimmed baking sheet, taking care not to break them into pieces. Discard the onion and garlic. In a colander set over a large bowl, 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, then transfer to a serving platter. Arrange the vegetables around the meat and drizzle with the cooking liquid, if desired. Serve hot or cold, with mustard or horseradish on the side.