XO Sauce is an interesting thing; I think this Wikipedia snippet is a good way to start –
Developed in the 1980s in Hong Kong for Cantonese cuisine, XO sauce is made of roughly chopped dried seafoods, including scallops, dried fish and shrimp, and subsequently cooked with chili peppers, onions, and garlic. This dried seafood-based sauce bears similarity to the Fujianese Shacha sauce. Spring Moon, the Peninsula Hong Kong‘s Chinese restaurant is often credited with the invention of XO sauce, although others claim the sauce’s origin in the urban area of Kowloon.[2]
