Rinse the cow tongue under cold water
Place it in a large pot and cover with water
Add salt, onion, garlic, bay leaves, and peppercorns if desired
Bring to a boil, then reduce to a simmer
Cook until tender, about 2.5 to 4 hours
Check tenderness by piercing with a fork
Remove the tongue from the pot and let it cool slightly
Peel off the outer skin while still warm
Trim away any excess fat or tough parts
Slice or chop the tongue as desired
Serve plain or use in tacos, sandwiches, stews, or other dishes