Work the zest into the sugar with the back of a spoon or with your fingers until the sugar is moist and fragrant.
In a bowl, cream the butter and sugar.
Add the egg, coconut flakes and key lime juice and mix until smooth.
Add the baking powder and flour, little at a time, mixing with a fork until the dough comes together. Form a ball, wrap it in cling film and chill it for 1 hour.
Preheat the oven to 350 degrees F (180 degrees C)
Take the dough out from the fridge and roll it into balls with your hands wet.
Roll the balls in granulated sugar first
and then in the icing sugar.
Place the coconut key lime crinkle cookies on a baking tray lined with parchment paper
and bake for 10 minutes.
When you take them out from the oven, place a chocolate chip on top, pressing gently while they are still hot.
Cool the coconut key lime crinkle cookies on the baking tray for about 5 minutes before transferring to a wire rack to cool completely.