Place ¼ of the basil in the shaker, crush gently with a wooden spoon. Add 50 ml of gin, 25 ml of orange liqueur, 2 tbsp of lemon syrup, 1 tbsp of lemon juice and 4 ice cubes. Seal the shaker and shake well for approx. 30 secs. Pour the cocktail through a sieve and into a glass, garnish with the reserved basil leaves. Repeat this step three more times.