Here is the way I do them. Very popular down at the local watering hole.
Beer – 1 bottle
2T chopped garlic
2 green onions, chopped
2 bay leaves
2t black pepper
Soak tongue in salted water for 2 or 3 hours in the refrigerator. Drain and replace with fresh cold water and continue to soak overnight, changing water once more.
Remove from the refrigerator and simmer soaked tongue in water and beer to cover, with the seasonings above for 1-1/2 hours.
Remove tongue to cool, then peel skin and trim fat. Season with a no-sugar beef rub, paint with a coating of mustard, add a little more rub.
Set up cooker for barbecue temperatures no higher than 250°, using pecan and apple wood. Add a slice of bacon on top. Prepare a basting sauce with apple juice, cider vinegar, oil, salt & pepper. Turn and baste every 30 minutes, moving the bacon to the topside on each turn. In about 2 hours the internal temperature will be 150°. Remove & cool.
Serve, sliced thin with horseradish sauce and/or ground mustard as an hors d’oeurve or on sandwiches.