To make the rub, add the juniper berries, peppercorns, chili pequins and fennel seeds to a clean coffee or spice grinder and grind together. Mix with the remaining spice rub ingredients.
Preheat the oven to 300°.
Generously rub the brisket on all sides with the spice rub. Heat the oil in a Dutch oven or heavy baking dish on medium heat until hot. Add the brisket and lightly brown on both sides.
Remove the meat and pour off the drippings. Return the brisket to the pan and add the beef stock. Cover tightly and cook for 3 to 4 hours. To serve, cut against the grain and cover with a brisket glaze, if desired.