Quarter the apple and remove the core. Roughly cut 1 quarter into cubes and put into the glass.
Pick the thyme leaves from one of the branches. Use the pestle to crush the apple and thyme until you get a kind of paste.
Fill ice cubes into the glass to the brim. Pour in the gin and tonic water and stir twice with a spoon.
Place the sprigs of thyme in the palm of your hand and clap firmly to release the essential oils. Cut apple quarters into thin slices.
Pierce the toothpick on the edge through the slices and place it fanned out on the drink. Put the thyme on the side in the glass.