In a small bowl, mix the softened cream cheese, chopped dill, lemon juice, salt, and pepper until well combined.

Using a sharp knife or a mandoline, thinly slice the cucumber. Pat the slices dry with a paper towel to remove excess moisture.

Spread a thin layer of butter on one side of each bread slice (if using). Spread a generous layer of the cream cheese mixture on the unbuttered side of four bread slices. Arrange the cucumber slices evenly over the cream cheese. Top with the remaining bread slices, cream cheese side down.

Using a sharp knife, carefully cut off the crusts from each sandwich. Cut each sandwich into quarters or halves and arrange them on a serving platter.