Stir-fry the oil in the bean paste and stir-fry the red oil. Add duck pieces and stir-fry over high fire. Add salt, oyster sauce, thirteen spices, soy sauce, star anise, dried pepper, etc. Pour a bottle of beer with the same amount of boiling water as duck. When the pot is boiled, turn to low heat and simmer. After the stew is cooked, add monosodium glutamate, coriander and chopped green onion and you can eat it.