Pre-heat your oven to 160C Fan/180C/350F/Gas Mark, and grease and line three 8" cake tins (that are at least 2" deep)
To make the sponge mix together the butter/baking spread and sugar until light and fluffy, around 2-3 minutes. For best results, use an electric mixer
Add the eggs and vanilla extract, and whiskmix them in
Then gently whisk or fold in in the self raising flour, baking powder and cocoa powder
Finally, fold in the chopped hazelnuts
Divide the mixture between the three tins, use scales for accuracy if you like
Bake them for 35-40 minutes or until a skewer inserted in the middle comes out clean. Leave them to fully cool either in the tins or on cooling racks
To make the buttercream, mix the butter on it's own for a few minutes, then add the icing sugar and mix until just combined, using an electric mixer for best results
Add the Nutella and mix it in, then add the milk, you can add extra milk if the buttercream is too stiff. Then put it in a piping bag fitted with the nozzle of your choice
Stack the sponges up on your plate or cake stand, piping buttercream between each layer, then drizzling the warmed Nutella over the buttercream. Start by going around the edges of the sponge, then fill in the middle
When you get to the last layer, pipe larger rosettes all around the edge and smaller ones in the centre
Sprinkle the chopped hazelnuts over the cake and place the Kinder Bueno pieces all around the edge. Drizzle with more Nutella
Store leftovers in an airtight container in a cool place and eat within 3 days