Cover the eggs with water in a medium pot. Bring the water to a gentle boil and boil for 1 minute. Remove from the heat and let stand for 12 minutes.
Drain the eggs and rinse them with cold water until the eggs are cool to the touch. Peel the eggs. Slice each egg into halves horizontally.
Place the cooked yolks in a mixing bowl and set the cooked egg whites aside on a serving tray.
Roughly mash the yolks with a fork. Stir in the mustard and truffle oil until smooth. Stir in the tarragon if using. Season with salt and pepper to taste.
Spoon or pipe the yolk mixture into the egg white shell. If the yolk mixture is too thick to spoon or pipe easily, stir in additional truffle oil or water a few drops at a time until the mixture is loose enough to pipe.