• Preheat your oven to 350F. Add the softened butter and sugar to a mixing bowl and cream together for around 2-3 minutes, or until fluffy and creamy. You can use your stand mixer or hand mixer for this.
  
• Now add the cocoa, vanilla and flour and mix until thoroughly combined. You can use your stand mixer or hand mixer for this.
  
• Add the cornflakes and stir in lightly using a spoon rather than your mixer. I recommend this so as not to break up your corn flakes.
  
• Shape your cookies by lightly rolling large spoonfuls (a little over a tablespoon) of dough into ball shapes. There should be enough dough to make about 20 cookies. Place these on a silicone baking mat or parchment paper which has been placed on a baking tray. Leave some room between the cookies as they will flatten when baking.
  
• Bake for around 13-15 minutes. They will be soft when removed from the oven. Leave them on the baking tray for 10 minutes, and then transfer to a wire rack to cool completely.
  

Making The Icing

• While the cookies are baking and cooling you can make your icing. Add powdered sugar, cocoa, melted butter, and vanilla to a large bowl and mix together thoroughly.
  
• Add the hot water a little at a time until you get the consistency of icing that you want. I used almost all of the 2 tablespoon of warm water for my icing.
  

Icing The Cookies and The Finishing Touch!

• Lightly toast the walnuts in a small skillet on medium heat.
  
• Ice the cookies. I used a small spoon and my fingers to spread the icing onto the cookies. Then top with a lightly toasted walnut half and try not to eat them all in one go!