Turn on the oven to preheat to 180 degrees. Cover two baking sheets with parchment.
With a mixer on medium-high speed beat the butter and sugar until creamy.
Continuing to beat at low speed, add flour and cocoa powder to the butter mixture.
Add cornflakes and coconut to the dough and stir with a spoon.
With a tablespoon, place the piles of dough on prepared baking sheets at a distance of 2.5 cm from each other.
Place the trays in a preheated oven and bake the chocolate chip cookies for about 15 minutes.
Put the finished chocolate chip cookies on a wire rack and let them cool.
Meanwhile, prepare the icing. Mix the icing sugar with the cocoa powder, add the vanilla extract, and enough boiling water to make a not very liquid icing.
Put the icing on the cooled biscuits and sprinkle chopped nuts over the chocolate biscuits.