Lightly butter one side of each bread slice with the softened unsalted butter. If you prefer crisped bread, heat a large skillet over medium heat, add 1 tsp olive oil, and toast buttered side down until golden, 1–2 minutes per side. Alternatively, toast the bread in a toaster until lightly golden. Set toasted slices on a cutting board, buttered side up.

Prepare tomato slices

Slice the tomato into 1/4-inch (6 mm) thick rounds. Lay slices on paper towels and sprinkle with 1/4 tsp kosher salt and 1/8 tsp freshly ground black pepper; let sit 1–2 minutes to draw out excess moisture, then blot dry.

Spread condiments

Spread mayonnaise evenly on the buttered side of four bread slices (about 1 tbs each). If using mustard, spread a thin layer on two of those mayonnaise-spread slices (about 1/2 tsp each). Leave two slices with butter only (these will be the outer slices).

Layer the first tier

On one mayonnaise-spread slice, place 2 leaves of lettuce (trim large leaves to fit if needed), then 2 slices of turkey arranged evenly, and 1 slice of cheese (if using). This forms the bottom tier.

Add middle slice and second tier

Place a second toasted slice (butter side up, no mayo) on top of the first tier to act as the middle piece of bread. On that middle slice, spread a thin layer (about 1/2 tbs) of mayonnaise, then add 2 more leaves of lettuce, the tomato slices (1–2 slices depending on size), and 4 bacon strips arranged to cover evenly. If using ham, add 2 slices here beneath or above the bacon. This creates the second tier.

Top and secure

Place the final toasted slice (mayonnaise side down if previously spread) on top of the second tier. Gently press the sandwich together. Insert toothpicks or sandwich picks through each quarter to hold layers in place. Using a sharp serrated knife, trim off crusts if desired, then cut the sandwich diagonally into four triangular quarters (cut twice to make quarters).

Serve

Arrange the four sandwich quarters on a plate with pickle spears. Serve immediately while bread is crisp and bacon warm.

Make-Ahead and Variations

To make ahead up to 1 hour: assemble without adding tomato (tomato makes bread soggy). Wrap tightly in plastic wrap and refrigerate. Add tomato slices and toothpicks just before serving. For a lighter version, substitute turkey with roasted chicken breast and use whole-grain bread.