Preheat the oven to 180C/350F/Gas mark 4. Grab a separate bowl and add the self-raising flour, unprocessed cocoa powder, baking powder and whisk until well combined. Set aside for later.
Whisk the unsalted butter and caster sugar in a bowl for 3-5 minutes or until it is nearly white in colour.
Crack the eggs open in a bowl and add 1 tsp of hazelnut. Add 1/4 of the eggs to the bowl and whisk well (until you can no longer see the eggs). Repeat this process for the rest of the eggs in the bowl.
Add half of the flour mixture to the butter mix and gradually add the milk. Use a large spoon or hand held whisk to mix all of the ingredients together. Repeat this step with the second half of the flour mixture until you get a silky consistency.
Grab some lightly greased 6" non-stick cake tins and use a spoon to add equal amounts of the cake batter to each tin. Place the tins in the oven on the middle shelf and leave to bake for 25-30 minutes. Stick a skewer in each cake and if the skewer comes out clean then the cakes are ready.
Leave to cool on a rack for 2 hours or until cool before you start decorating.