1. Wash pork leg in clean water, then grill until the skin is golden. Use a sharp knife to rub off all tough hairs. Wash again and cut into well pieces.
2. Heat soup in a big pot over low heat. Add lemongrasses, chilies, kaffir lime leaves, and pork legs. During this time, occasionally remove the dirt, bubble and excess oil that float up.
3. Wait until boiling then add mushroom. Stir until all ingredients mixed well and the pork leg is done. Then season with sugar and fish sauce. Remove from heat.
4. Transfer to a serving bowl. Serve immediately with hot steamed rice.
(For 2 Serving)