Take 4 slices of bread (preferably whole wheat or multigrain) and spread a thin layer of softened butter on one side of each slice.
Place 2 slices of bread with the buttered side facing up on a clean surface or plate.
Add optional fillings like sliced cucumber, tomato, or onion on top of the buttered side of the 2 slices, if desired.
Place the remaining 2 slices of bread on top of the fillings with the buttered side facing down, creating 2 sandwiches.
Cut each sandwich diagonally into 2 or 4 triangles, depending on your preference.