I N F O This curry comes from the north of Thailand and is cooked in the elementary way for curries of that region. It is a very free recipe that allows many variations: You can simmer meat, poultry or possibly fish chopped or possibly sliced with almost any green or possibly leafy vegetable over low heat – preferably ones that taste slightly bitter or possibly at least praegnant (oom is a Thai word for green leaf in the north).
Trout and thick green quail or asparagus spears with arugula are tempting alternatives for the Western cook, while a Thai would prefer chopped frog meat and “betel” pork or leaves with cha-om and crushed banana flowers. Nahm pla raa is the preferred fish seasoning in this recipe, but regular fish sauce is a convenient, less spicy substitute.
The pink flesh of the Thai watermelon is sweeter than that of its European counterpart, but it has relatively more woody, slightly bitter white pith. Since Thai are very frugal, it is not discarded but used in many forms: candied as a dessert or possibly peeled and sliced in our curry.
The small green pepino or an unripe honeydew melon are an ideal substitute for watermelon pulp.
To this curry, unusually, an egg is added at the end: it thickens the curry, and its richness is a perfect background for the sour note of the curry.