Boil the brown sugar with 200ml water. Add the lemongrass and ginger and cook gently for about 3 minutes.
Remove the pot from the stove and place the lemon balm in the broth. Leave closed for about 10 minutes.
Pour the ginger-lemongrass stock through a sieve and leave to cool. Squeeze the limes and add the juice to the syrup. Then chill in the fridge until further use.
It serves:
Quarter the apple, cut out the core and cut into thin wedges.
Place the apple wedges and Thai basil in a pitcher or separate into individual glasses. Pour the mineral water over the lemongrass ginger syrup and enjoy over ice cubes.