Line two baking trays with baking paper, and pre-heat your oven to 180 degrees C.
Start the biscuit dough by creaming the butter and sugar together with hand beaters or using a stand mixer until light and fluffy.
Add the flour, salt and sifted cocoa powder and mix on low until combined.
Add the cornflakes and mix until evenly combined.
Shape the biscuits by rolling heaped teaspoon-sized portions into balls, gently flatten, and place on your prepared trays.
Bake for 15-20 minutes, rotating the trays halfway through the baking time.
Leave to cool to room temperature on the trays.
Once cooled, make the icing by mixing 160g of the icing sugar, sifted cocoa powder, butter and half the liquid until combined.
Dollop and spread spoonfuls of the icing on each biscuit, and finish with a single walnut.
Store in an airtight container for up to a week.
