In a small bowl, stir together the eggs, watercress, mayonnaise, salt and pepper with a fork till well mixed. Mix in olives, if you like.
Trim crusts from bread. Butter 1 side of each slice. Spread the egg mixture on 2 of the buttered bread slices. Top with remaining bread slices, buttered side down. Press lightly together.
Cut each of the 2 sandwiches into 3 fingers. Secure with toothpicks decorated with olive pieces, if you like. Arrange on a serving platter. Makes 6 servings.
