Thinly peel the lime zest using a peeler, twist. Pour half of the gin, 1 espresso, 3 tbsp of syrup, the juice of one lime and 1 egg white into a shaker, top up with ice cubes. Seal the shaker and shake well for approx. 30 secs. Divide the ice cubes between the glasses, pour the cocktail through a sieve into 2 glasses. Repeat the process. Decorate the glasses with the lime zest.