Fill an instant pot or slow cooker with onions, tongue (and stew meat if using), tomatoes, garlic, bay leaves thyme and 2 tablespoons salt.
If slow cooking, cook for 3 hours. If using instant pot, cook for 90 minutes. Tongue should be soft and tender with the outer layer peeling off.
Remove tongue and bay leaves from the pot. Discard the bay leaves. Place the rest of the pot contents into a blender. Blend until smooth and then pour into a medium pot. Place pot on stove top over high heat to reduce the water content. The sauce will thicken as it reduces. Reduce the pot but about half.
While the sauce is reducing, place tongue on a cutting board. Remove the outer layer and discard. Chop or shred the meat. Add some more salt to taste and place shredded meat on baking tray. Place tray under broiler to crisp for 5-7 minutes minutes. Keep an eye on the meat to ensure it doesn’t burn.
Place crispy meat in a bowl. Toss in an appropriate amount of the reduced sauce from the pot. Mix well, sprinkle with 1-2 tablespoons Pluck seasoning and serve with the taco add-ons that fit your palate.
Soften the tortillas on the stove-top in a dry pan about 5-10 seconds per side.