Melt the milk and dark chocolate in a large heatproof bowl set over a pan of barely simmering water, taking care to ensure that the bowl doesn't touch the water. Once the chocolate has melted, remove from the heat.
Using either an electric or hand-held whisk, whip the cream until it just holds its shape.
Gently fold the cream into the melted chocolate. Divide among ten mini glasses or flowerpots and chill in the fridge for 2 hours or until set.
Blitz the cookies to a fine crumb in a food processor. Just before serving, sprinkle the crumbs over the top of the chocolate and insert a mint sprig into the centre of each flowerpot, so that it looks like a little plant.