OVER THE PAST SEVERAL DECADES, we’ve experienced a remarkable renais-sance of heirloom tomato varieties. For many of us, this has been our first opportunity to discover the wonderful, intense flavors of “true tomatoes,” which are unlike the tomatoes we find in the grocery store during winter months. Those have been bred for mechanical harvesting, shipping, and shelf life, and they often have a plastic taste. Heirloom varietals such as Gulf State, Oxheart, Pineapple, Ponderosa, Winsall, and 1884—to name just a few of my favorites—are juicier with complex flavors that range from sweet to spicy to tangy. Perhaps what I look forward to most during tomato season are the sandwiches. A perfect one requires only three things: white bread, Duke’s mayonnaise, and a thick slice of an heirloom tomato.…