Preheat the oven to 300°F (150°C).
Rinse the corned beef brisket under cold water.
Combine mustard seeds, black peppercorns, coriander seeds, garlic, and olive oil in a bowl.
Rub the spice mixture over the brisket generously.
Place the brisket in a roasting pan and pour the beef broth around it.
Cover the pan with aluminum foil and roast for 2.5 to 3 hours.
Remove the foil and increase the oven temperature to 375°F (190°C).
Continue roasting for an additional 30-45 minutes, basting every 15 minutes.
Remove from the oven and let it rest for 15 minutes before slicing.
Slice against the grain and serve with garnishes.
