Fried Cod with Tomato Salad and Serrano Mayonnaise

This dish was inspired by one from Sisha’s native Chile: a fried fish with a traditional tomato and onion salad. In Chile, the onion is not a condiment in the salad but, rather, an ingredient in its own right. So as not to be overpowered by so much raw onion, we “shock” the onion first; this blunts the thrust of the onion without sacrificing its texture. The sparkling water in the batter lends a tempura-like quality. And since the traditional Chilean green chile is unavailable here, we use serrano chiles—smaller and about five times hotter than jalapeños, but thin-walled and easy to use.