Hard-boiled eggs, deep-fried until the exterior is golden and slightly blistered, topped with a sweet-sour tamarind-fish sauce dressing, crispy fried shallots, and dried chilli. Khai luk koei ('son-in-law eggs') is a preparation that transforms a hard-boiled egg — by deep-frying — into something with a complex textural range: the crispy, blistered exterior of the deep-fried egg white giving way to the completely set, dense interior, all dressed with the sweet-sour tamarind sauce. It is one of the most clever of all Thai preparations in its use of a secondary cooking technique (deep-frying a pre-cooked egg) to achieve a result impossible by either method alone.
**The hard-boiled eggs:** - 7 minutes from boiling: white fully set, yolk just-set with no grey-green ring. - Cool in cold water, peel carefully. - Dry thoroughly before deep-frying — surface moisture causes violent spattering. **The deep-frying:** - Oil at 180°C in a wok. - Lower the peeled, dried eggs gently into the oil. - The egg white's surface proteins, already fully coagulated from boiling, begin to brown and blister at this frying temperature — producing a lacy, slightly blistered golden exterior. - Fry for 3–4 minutes, turning carefully. - The interior (white and yolk) is already cooked — the frying only affects the exterior. **The tamarind dressing:** - Tamarind water (Entry TH-18): 3 tablespoons. - Palm sugar: dissolved, 2 tablespoons. - Fish sauce: 1 tablespoon. - Cook together in a small pan over medium heat until slightly reduced and thickened — the palm sugar caramelises with the tamarind and fish sauce, producing a dark, glossy, sweet-sour-salty sauce. - Pour hot over the fried eggs at service. **The garnish:** Crispy fried shallots (Entry TH-48), dried chilli flakes (briefly dry-roasted), fresh coriander. The contrast of the caramelised sauce, the crispy shallots, and the blistered egg surface is the preparation's complete sensory range. Decisive moment: The tamarind sauce at the correct reduction — thick enough to coat the eggs and pool at the base of each serving plate, thin enough to pour. Reduced too far: the sugar crystallises as it cools and the sauce turns grainy. Too thin: it runs off the egg and the dressing is not present in each bite. Sensory tests: **Sight — the fried egg surface:** The correctly deep-fried egg has a blistered, golden-amber surface — irregular, slightly textured, far from the smooth white of a boiled egg. The blistering (formed by the steam from the egg white's internal moisture attempting to escape through the protein layer) is the visual signature of the preparation. **Taste:** The combination of the dense, rich, slightly rubbery (in the best sense) fried egg white, the blistered exterior's slight crispness, the dark sweet-sour tamarind sauce, and the crunch of the fried shallot: one of the most complete single-bite experiences in Thai cooking.
David Thompson, *Thai Food* (2002); *Thai Street Food* (2010)