For the ice cream, combine the cream and milk in a heavy saucepan, add the 50g of Westlands chocolate mint and bring to a simmer. Cover and leave to infuse for 30 minutes. Whisk the egg yolk with the sugar and then reheat the milk and cream. Whisk the cream mix onto the egg yolks and then return to the pan. Cook out over a gentle heat stirring constantly. Cook until the custard starts to thicken and has reached 79℃. Pass through a fine chinois and chill. Churn in an ice cream machine.
For the cookies, cream the butter with the sugars and syrup. Gradually beat in the egg and yoghurt. Sift the flour, cocoa, baking powder and salt together and fold into the butter mix. Stir through the chocolate. Scoop 12 balls from the mix and place, widely spaced, on a silpat mat. Spread slightly with the back of a wet spoon. Bake at 170℃ for 10-12 minutes until the cookies are risen and firm around the edges. Transfer to wire rack to cool.
To serve:
Scoop small balls of ice cream onto half the cookies and then sandwich together with the remaining cookies. Serve immediately.