Rinse the pickled beef brisket under cold water
Place the brisket in a large pot
Add enough water to cover the meat
Bring to a boil
Reduce to a simmer
Skim off any foam
Add onion, garlic, bay leaves, and peppercorns if desired
Cover and simmer until tender, about 3 to 4 hours
Check occasionally and add more water if needed
Test tenderness with a fork
Remove the brisket from the pot
Let it rest for 10 to 15 minutes
Slice against the grain
Serve hot