Deep-frying is a method I prefer to avoid for everyday cooking, but this is one of the dishes for which I make an exception. When served, it tends to provoke that moment of rapt, intense silence at the dinner table that is one of the tokens of true appreciation. Slices of chicken thigh meat are first deep-fried in a light batter, then tossed in a sophisticated sweet-sour sauce laced with chile. General Tso's chicken is supposedly a Hunanese dish, but it's virtually unknown in Hunan Province. It was actually invented by Peng Chang-Kuei, a Hunanese exile chef in Taiwan, and cooked by him in his one-time New York restaurant. It has since been taken so much to the heart of Americans living in the northeast that it is now known as the very essence and emblem of Hunanese cuisine. This version of the dish is based on the recipe I learned in Peng Chang-Kuei's kitchen in Taipei.
The dish is usually made with boned chicken leg meat, although you can use breast if you prefer. Do make sure your wok is stable before using it for deep-frying: it's important to use a wok stand with a round-bottomed wok.
Combine all of the ingredients in a small bowl.
Unfold the chicken thighs and lay them, skin side down, on a cutting board. (If some parts are very thick, lay your knife flat and slice them across in half, parallel to the board.)
Use a sharp knife to make a few shallow criss-cross cuts into the meat — this will help the flavors penetrate. Then, cut each thigh into 1 ½- to 1 ¾-inch-long slices, an uneven 1/8 inch or so in thickness. Place the slices in a bowl.
Add the soy sauces and egg yolk to the chicken and mix well. Then stir in the potato flour, and lastly 2 teaspoons of the oil. Set aside.
Place a wok over high heat and line a plate with paper towels. Add just enough oil to submerge the chicken (you may need to do this in batches) and heat to 350-400 degrees. Add the chicken and fry until crisp and golden. Remove the chicken with a slotted spoon to the paper towels. Pour the oil into a heatproof container and clean the wok if necessary.
Return the wok to high heat. Add the remaining cooking oil and the chiles and stir-fry briefly until they are fragrant and just changing color (do not burn them). Toss in the ginger and garlic and stir-fry for a few seconds more, until you can smell their aromas. Then add the sauce and stir as it thickens.
Return the chicken to the wok and stir vigorously to coat the pieces in sauce. Stir in the sesame oil, then serve, with a scattering of scallions, if using.