The bread should be white and toasted; Pullman or packaged sandwich loaf works best. This kind of bread has a soft, tight crumb that will soak up some of the tomato's juices, and toasting it helps prevent it from becoming overly sodden. The bacon must be smoked, to adequately offset the tomatoes' sweetness. I like a medium-thick cut, and I take care as I cook to avoid a result that's desiccated or leathery; the latter impedes biting through the sandwich's layers with ease and tasting all the ingredients in each mouthful. Crisp iceberg lettuce lends the right note of freshness, and the tomatoes should be absolutely ripe and sweet. Mayonnaise is not optional; its creaminess tempers the tomatoes' acidity. The matter of whether to slice your BLT into triangles or rectangles, however, is up to you.