Preheat the oven to 180℃

In a large mixing bowl, add the flour, caster sugar and cocoa powder. Mix well.

In a saucepan, add the butter and heat over a medium heat until fully melted.

Pour the butter into the dry ingredients and mix until its well combined. You might prefer to get in there with your hands. It should resemble a crumb mixture.

Press the crumb mixture down into a lined 20 cm baking tin. Press it down firmly so it compacts.

Place it in the oven for 20 minutes.

Once done, take it out and set it aside to cool, sprinkle some caster sugar over the top.

Once cooled, cut it into portions.

To make the mint custard, mix the cornflour with the sugar then add a splash of the milk. Mix until its a loose paste like mixture.

Place the rest of the mik into a saucepan and heat over a medium heat. Add the cornflour paste and carry on cooking over a medium heat. Stir continuously until it thickens.

Once it has thickened to the right consistency, add a splash of peppermint extract and the green food colouring. Mix well.

Serve the concrete cake and pour the mint custard over the top.