1. Grind garlic, peppercorns, coriander roots and salt in a mortar and pound until mixed thoroughly (or using food processor).
2. Heat oil in a wok over medium heat and add the ground mixture (prepared in the 1st step). Fry until aromatic then add some water.
3. Add sugar, black soy sauce, tamarind concentrate, ginger and chilies. Stir fry until all ingredients mixed well. Add prepared mackerel fish and turn to low heat. Let simmer for at least 30 minutes.
4. Transfer to a serving bowl (or plate). Garnish on top with coriander leaves. Serve immediately with hot steamed rice.
(For 2 Serving)