Prepare a double espresso and leave to cool. Fill up a 200ml glass with ice
Half the lime, and squeeze the juice from one half, then cut the other into wedges and save one for later, freeze the rest for ice cubes or pack up and pop in the fridge for later use. Pour the lime juice over the ice. Then pour in the tonic water, so that your class is about 2/3 full.
Then pour in the slightly cooled double espresso, add the lime wedge on top. Sip away and enjoy your very own espresso tonic.