Boil the Ox tongue in about 1 quart of water for 90 minutes or until tender (you can use a pressure cooker to quickly tenderize it).
Let the tongue cool down, and then scrape out the skin.
Slice the tongue into serving pieces.
Heat oil in a cooking pot.
Saute onion and garlic.
When the onion becomes soft, put-in the Ox tongue. Cook for 3 minutes.
Add oyster sauce, soy sauce, sugar, and Worcestershire sauce. Stir and then simmer for a minute.
Add the mushrooms and Pour-in water. Let boil and then simmer until the liquid reduces.
Add salt and pepper to taste.
Put-in the cornstarch and water mixture. Stir. Cook until the sauce thickens.
Transfer to a serving plate. Sprinkle parsley flakes on top.
Share and enjoy!