In a small bowl, combine the eggs, bacon and tartar sauce. Cover and refrigerate for 30 minutes.
Using a 2-1/2-in. bell-shaped cookie cutter, cut out two bells from each slice of bread. Lightly spread one side of each bell with butter. Spread egg mixture over half of buttered bells; top with remaining bells, buttered side down.
If desired, garnish each sandwich with an olive slice, securing with a small amount of egg mixture. Cover and refrigerate until serving.