Dry shake or whisk the egg white until emulsified, before adding the remaining ingredients and filling the shaker with ice. Cap, give it a brief but hard shake before double straining into a chilled coupette. Garnish with a trimmed spring of fresh tarragon.
Earl Grey Tea Syrup:
Steep 1 tbsp loose Earl Grey tea leaves in 150ml boiling water for 3 minutes. Strain out the leaves and heat the liquid with an equal amount of white caster sugar until dissolved. Allow to cool, bottle and store in a fridge for up to two weeks.