Occasionally, a few sauces stand out in my mind, and this is definitely in the top five: tart, smoky, spicy-hot, and appealing to look at. Credit goes to the blackish-purple fruit of the kokum family, smoked and dried, which gives this curry its distinct flavor. During a recent stay at the Coconut Lagoon resort in Kumarakom, Kerala, I attended a cooking class on a hot, lazy afternoon. Strikingly handsome, tall, and thick-mustached, with his tall French chef’s hat perched on his charcoal-bla