3 strips thick-cut, naturally cured bacon (see note)
2 slices high-quality sandwich bread, such as shokupan
2 tablespoons (30ml) homemade or store-bought mayonnaise (see note)
1 cup finely shredded iceberg lettuce (from about a quarter head; see note)
2 to 4 thick slices ripe tomato (see note)
Coarse sea salt, such as fleur de sel or Maldon
Freshly ground black pepper
Place a griddle or skillet over medium-low heat. Add bacon and place a bacon press, skillet, or masonry trowel on top of it to keep it flat as it cooks. Cook until lightly browned on first side, about 5 minutes, then flip, cover again, and continue cooking until bacon is browned on both sides and fat has rendered, about 3 minutes longer. Transfer bacon to a paper towel–lined plate and set aside.
Place bread on same skillet or griddle and toast in bacon fat over medium-low heat, swirling occasionally, until evenly browned on first side. Flip and brown second side.
Lay toasted bread on a work surface and spread mayonnaise on both top faces. Divide lettuce evenly between both pieces of bread. Layer tomato slices on 1 piece of bread and sprinkle generously with coarse salt and freshly ground pepper.
Break bacon slices in half and layer them onto the sandwich in 2 layers of 3 half slices each, alternating the orientation of bacon in each layer for more structural stability. Close sandwich and cut in half diagonally. Serve immediately.