From Pinoycook.net 
Ingredients :
1 ox tongue (about 1.1 kilos)
2 tbsp. of vinegar
1 whole garlic
1 whole onion
6 peppercorns
1 bay leaf
1/2 carrot
a few stalks of leek
1 can condensed mushroom soup
1/4 c. + 2 tbsp. of butter
1 onion, chopped
1/2 k. of potatoes
1/2 c. of milk
salt and pepper
1 tsp. of finely chopped fresh parsley
1 onion, sliced
4 button mushrooms, chopped
How to :
Scrape the ox tongue with a knife. Rinse well under running water. Place in a glass bowl and cover with water. Add 2 tbsp. of vinegar. With your hands, “wash” the tongue in the warer-vinegar solution. Rinse well. Place the ox tongue in a casserole and cover with water. Pierce garlic in several places with a sharp pointed knife. Add garlic, onion, carrot, leeks, peppercorns and bay leaf to the tongue. Set over medium heat and bring to a soft boil, removing scum as it rises. Lower heat, cover and simmer until tender, about 4 hours.
While simmering the meat, prepare the mashed potatoes. Using a brush, scrub the potatoes under the tap, making sure that no soil remains. Place the potatoes in a saucepan and cover with water. Add 1 tsp. of salt. Set over high heat and bring to a boil. Lower heat, cover and simmer until tender. To test for doneness, insert a pointed knife at the thickest part of the potatoes. Drain the potatoes and transfer to a glass bowl. Cut the potatoes into small pieces. Mash with a fork (I did not remove the skin). Add 2 tbsp. of butter and mix well. Season with salt and pepper. Pour in 1/2 c. of milk in a thin stream. Blend well. Stir in the chopped parsley. Cover the bowl with a cling wrap.
When the tongue is tender, transfer it to a plate and cool completely. Remove the skin and slice crosswise into 1/4? thick slices. Set aside. Strain the broth.
Over medium-high heat, melt 1 tbsp. of butter in a skillet. Brown the chopped onion. Remove with a slotted spoon and drain on paper towels. Set aside.
Increase heat to high and melt the remaining butter in the skillet. Add the sliced lengua and brown them in batches, removing them as they brown and adding more butter if necessary. Saute the sliced onion in the skillet. Add the chopped mushrooms. Dilute the mushroom soup with the meat broth. Use equal parts of soup and broth for a regular sauce; reduce the amount of broth by half for a thicker sauce. Pour diluted soup into the skillet. Lower heat to medium and bring to a soft boil, stirring to make sure that no lumps remain. Return the tongue slices to the skillet and heat through.
Serving suggestion:
Spoon the mashed potatoes at the center of the serving plate (see photo above). Top with the browned onion bits. Arrange the meat slices on both sides of the mashed potatoes. Pour the sauce over the meat. Serve hot.
Breakfast 
