How to Make It
In a large nonstick skillet, heat 1/4 cup of the oil. Add the ginger and garlic and cook over moderate heat, stirring, until golden, 10 minutes. Scrape into a bowl.
Heat another 1/4 cup of the oil in the skillet. Add the shallots, onion and chiles; cook over moderately low heat, stirring, until golden, 15 minutes. Scrape into the bowl.
In the skillet, cook the dried shrimp in the remaining 1/4 cup of oil over moderately low heat, stirring, until golden, 10 minutes. Add the contents of the bowl to the skillet along with the vinegar, tamarind, cumin, chile powder and bay leaves. Cook over low heat, stirring, until slightly thickened, 15 minutes. Discard the bay leaves and let cool.
Dried shrimp and tamarind concentrate are Thai ingredients that are both available at Asian markets.