Preheat your oven to 160C/140C Fan and line a 9x13" Tin with parchment paper.
In a heatproof bowl, microwave the Dark Chocolate and Butter till melted - I do mine in 30 second bursts!
Add your Coffee Granules and Malt Powder to a small bowl, and add in 150ml Boiling Water. Whisk till smooth!
Add this to your Chocolate/Butter mix and whisk again till smooth.
In a large bowl, add your Plain Flour, Cocoa Powder, Baking Powder, Bicarbonate of Soda, Golden Caster Sugar and Light Brown Sugar and whisk till distributed evenly!
Whisk the Eggs and Buttermilk together till smooth.
Add your melted Chocolate mix to the bowl, and your Egg/Buttermilk mix, and fold all the ingredients together till they are combined - I use my hand and a spatula, and not an electric mixer as I don't want the ingredients to over mix.
Pour the mixture into the lined tin, and bake in the over for 50-60 minutes, or until baked through.
Leave to cool in the tin for 10-15 minutes, and then on a wire rack fully!
For the Decoration!
With an electric mixer, beat your butter on it's own for a few minutes so it's lovely and supple.
Add in your Icing Sugar 1/2 at a time and beat for a few minutes!
Add in your Malt Powder, and beat again - if its stiff, add in 1tbsp of Boiling Water at a time and beat fully each time till its a thick but spreadable and smooth consistency!
Spread over the cake with an angled spatula, and then sprinkle over some Maltesers and some crushed Maltesers!
This cake will last for 3-4 days+ at room temperature in a cake box!