The fried green tomato BLT changes one component of the BLT and in doing so fixes the BLT's oldest structural flaw. A ripe tomato is the wet, fragile part of a BLT: it floods the toast, slides under the bacon, and turns a precarious sandwich soggy before it is finished. Swap in an unripe green tomato, sliced thick, dredged in cornmeal, and fried, and that liability becomes the spine. The fried slice is firm, tart, and crisp-shelled, so it holds its shape against the bacon, brings its own acid in place of the ripe tomato's juice, and adds a hot crunchy layer the plain BLT never had. The green tomato is the defining swap, and it does structural work rather than merely standing in for the ripe slice.
The craft is in the dredge and the order of the stack. A green tomato is dense and sour, so it is cut thick and given a buttermilk soak and a cornmeal coat that fries into a sandy, gritty shell with a faint corn sweetness, the same coating logic a fried catfish leans on, used here against bacon instead of fish. Cornmeal matters: it crisps without going greasy and it stays crisp longer than a flour batter under the steam of a warm filling. The toast still has to be crisp and the bacon still has to be the load-bearing flavor, but the mayonnaise now seals the bread against a coated slice rather than a leaking one, and the lettuce is the only purely cold element left. The fried slice goes in warm, straight from the pan, so its shell is still set when the sandwich reaches the hand, because a fried green tomato that sits softens from the inside the way any fried thing does. It is a Southern lunch-counter build, assembled fast and eaten hot, and the speed is part of the recipe.
The variations stay inside that fried-slice, stacked frame. Some builds keep a ripe tomato alongside the fried one for sweetness against the tart; a pimento-cheese version trades the mayonnaise for a sharper bound spread; a club-style three-decker braces the stack with a middle slice the way the club braces a plain BLT. Each of those is its own codified build and deserves its own article rather than being crowded in here.