Place the mint leaves,water, sugar and peppermint and vanilla essence in a small pan and gently heat to dissolve all the sugar.
Transfer to a blender and blend until the liquid is completely smooth and green.
Return to the pan while it is still hot and add the gelatin. Stir until the gelatin has completely dissolved through the mint mixture.
Fold the yoghurt into the mix then pour it into 6 x 1/2 cup jelly moulds or ramekins.
Place in the fridge for about 3 hours to set.
Break the chocolate into a glass or metal bowl. Fill a pan with about 3 cm of water and bring to the boil. Turn off the heat then place the bowl over the pan and leave it to sit for about 5 minutes until the chocolate has melted.
To remove the jelly from the mould, place the dish in a small bowl of hot water for about 30 seconds. Turn it over onto individual plates and spoon a little chocolate over the top of each.