hen Ernest Hemingway dreamed of trout, he dreamed of it this way: cooked “au bleu,” as he first encountered it in Switzerland, which “preserves the trout flavor better than almost any way of cooking.” It’s rarely encountered that way, nowadays, for one chief reason: In order for the trout to turn blue, the fish must be killed almost immediately before cooking. (The color change derives from a chemical reaction between vinegar’s acid and the trout’s slime coating.) For anglers willing to keep their trout alive (or as fresh as possible), this isn’t an obstacle. If you’d like to prepare this as a Hemingway-esque streamside lunch, try skipping the salad. Make the court bouillon ahead of time, and transport it in a clean jug. Bring it to a boil in a pot over a campfire and proceed as directed.