Start by taking the tongue and adding it to a large saucepan. Add water and make sure it covers the tongue by a couple of inches. Place this on medium heat, and boil for about 2 hours.
After 2 hours, remove the tongue and place onto a cutting board. Pour the water out and wash out the saucepan.
Return the tongue back to the pot, cover with water again, then add in your aromatics. Add the jalapenos, black pepper, salt, bay leaves, piquin, quartered onions, garlic, and cilantro stems. Bring this to a simmer, and cook for 4 hours.
After 4 hours, remove the tongue, and strain the stock. Discard the stock solids, but reserve the stock (it’s really great).
Next, take the tongue and rinse under cold water. Now it’s time to peel the outer layer as that is not desired. If you cannot easily peel it, use a pairing knife and trim all of it away, exposing the cooked beef tongue.
Discard the outer layer, then cut your beef tongue into strips, then into bite-sized chunks. Season with a pinch or two of salt. Mix, and get ready to sear it up for your tacos.
Heat a large skillet on medium heat, then add a tablespoon of oil. Once heated, add in some of the beef tongue, and cook until it gets a slight sear on them. Once seared, add a spoonful or two of the reserved stock. Heat through until the stock reduces, then remove from the heat.
Take a flour tortilla, load it with some of the beef tongue, and top with cilantro and onion. Squeeze some lime, and dig in.