Turn the oven onto 180°C bake and line a cupcake tin with 12 cupcake cases, and then set aside.

Add the flour, cocoa, sugar and baking soda into a medium sized mixing bowl. Then, chop up the chocolate and walnuts until they roughly resemble a coarse breadcrumb texture. Add this in with the other dry ingredients and mix everything together.

Using a free-standing mixer or in a medium sized bowl with a hand-held beater, mix together the oil, buttermilk, eggs and cooled coffee. To make the cooled coffee, simply add ½ Tablespoon of instant coffee to 120mls of water. Beat these wet ingredients together until well combined.

While still beating, slowly add the dry ingredients in with the wet until everything comes together as a smooth mixture. Then, pour mixture into a jug and carefully fill cupcake cases to just over two-thirds full.

Bake for between 16-20 minutes or until the cupcakes spring back when touched and/or skewer comes out clean. Remove cupcakes from the oven and let them cool completely before making the buttercream.

When it's time to make the buttercream, melt the chocolate in a heatproof bowl over a pot of simmering water or in a microwave. Once melted, leave chocolate to cool for 5-10 minutes.

Meanwhile in a medium sized bowl, beat the butter with a hand-held beater (or using a free-standing mixer) for 5 minutes, scraping the sides down occasionally. Sift the icing sugar and then add to the butter in two stages, beating for another 3 minutes between additions.

On a slow speed add in the milk, then beat on high for another 5 minutes. Then, slowly pour in the melted chocolate and continue to beat for a few more minutes.

Once the cupcakes have cooled, pipe a big round blob of chocolate buttercream on the top of each cupcake and roll or press the crunchy cornflakes over and around the top. Enjoy.