A properly put together BLT is the Bruce Lee of sandwiches. It’s lean and light and full of fight. Just a few strips of bacon is all the meat there is on the bones of this black-belt combination of tomato, onion, mayo, bacon, bread, and lettuce. By using finesse and precision instead of brute force, that elegant BLT can whoop a reuben, a turkey Swiss, a roast beef, you name it—maybe all at once. It is a masterpiece of a sandwich, and a masterclass in all-around sandwich-ology, in part because pulling off a perfect BLT is not easy. The challenges inherent to a BLT pave the way for some of the most illuminating lessons in sandwich-making, as we get around the many pitfalls it presents. For example, consider the watery combination of tomato and mayo, a threat to the integrity of the bread. This combination is non-negotiable. That the tomato …