Grease and line a lamington tin and preheat your oven to 160C Fan / 320F.
Sift together the flour, cornflour and baking powder and mix well.
Beat together the sugar and butter until very light and fluffy. Add the eggs one at a time beating very well between each. Add the vanilla, zest and juice and beat again. Add flour mix and milk and gently fold through with a spatula, until just combined.
Spread the batter evenly in prepared tin. Bake for 18-20 minutes until just cooked (a toothpick inserted should come out with just a couple of crumbs). Allow it to cool slightly, then turn out onto a wire rack to cool completely. Trim edges off then cut into 20 squares.
In a wide bowl combine the coconut, zest, mint and icing sugar and mix thoroughly.
Combine the milk and chocolate in a small saucepan over low heat and stir constantly until the chocolate is almost melted. Pour the lime juice into the icing sugar then add the chocolate milk mixture. Stir until smooth. Using 2 forks, drop cake squares into the glaze and coat well. Allow excess to drip off then roll it in the coconut mixture. Place them in the fridge to set.