Preheat the oven to 160°C and grease and line a 20cm square loose-bottomed cake pan with baking paper.
Place butter, cocoa, sugar, eggs and flour in a bowl and mix well to combine. Press firmly into the prepared pan and bake for 15 minutes or until set. Allow to cool completely.
Meanwhile, for the mint topping, place sugar, mint and 1/2 cup (125ml) water in a saucepan over low heat and stir until the sugar dissolves. Increase heat to medium and simmer for 3 minutes, then set aside to cool completely. Strain the sugar syrup into a jug, discarding the solids. Place the cream cheese in a food processor and whiz for a few seconds to soften. Add cooled sugar syrup, eggs, peppermint extract, cream and food colouring and process until smooth.
Pour the cheesecake mixture into cake pan then tightly wrap the base of the pan with foil to make it watertight. Place the cheesecake in a deep baking dish and fill with enough boiling water to come halfway up the sides of the cake pan. Bake for 25 minutes or until topping is just set – the cake may have a slight wobble but it will firm on cooling. Remove from the oven and cool completely, then chill for 2 hours or until firm.
Cut cheesecake into slices, drizzle over the cooled melted chocolate and serve.