In a stockpot, place the ox tripe, beef skin, lemon grass and enough water to cover the meat.
Season with salt and peppercorns. Once the liquid boils, remove the pot from the stove, strain the liquid and throw it away.
In another pot, place the boiled ox tripe and beef skin.
Add pineapple juice, beef stock, ginger, bay leaf and season with salt and pepper.
Let boil until the ox tripe and beef skin are tender. When tender, remove the ox tripe and beef skin.
Cut both into strips then set the ox tripe, beef skin and stock aside.
To make the gravy, put butter and flour in a pan. Mix well then add chicken stock.
Whisk to smoothen the mixture and season to taste.
In a wok, heat the oil then saute the onion, garlic and tomatoes.
Add the tomato paste and heat until cooked. Add a little reserved stock from the pot, then add the ox tripe and beef skin. Simmer for 5 minutes.
Add the rest of the reserved stock, boil for a while, then add the tomato sauce, mushrooms and gravy.
Cook for a few more minutes then add the finger chilies, black and green olives. Adjust seasoning before serving.