Preheat the oven to 180oc/160oc fan and line a muffin tin with 12 cupcake cases. Place a heatproof bowl over a pan of barely simmering water and ensure the bowl does not touch the water. Add the butter and slowly melt before carefully lifting the bowl off the heat and stirring in the chocolate with a heatproof spatula. Once melted together, add the caster sugar, Nutella and eggs and stir until thick and chocolatey. Fold in the flour and add the milk to loosen the mixture slightly. Spoon roughly one tablespoon of batter into each case until the tray is filled. I had a little leftover so filled two more cases and set aside to bake later as I only have one muffin tin. Place the tray on a rack in the middle of the oven and bake for 20-25 minutes until a skewer comes out clean. Leave to cool in the tin for 10 minutes then remove each cupcake and cool completely on a wire rack. Bake any remaining cupcakes.
To make the frosting, beat the butter in a large bowl or stand mixer using the paddle or beater attachments for around five minutes until pale. Add the chocolate, taking care that it is cool or it will split the frosting. Beat together until creamy then add the cold coffee and Nutella and beat again. Add a good pinch of smoked sea salt to balance the sweetness a little then refrigerate the frosting for around 20 minutes to firm up slightly to make it easier to spread.
Place the hazelnuts on a baking tray lined with baking parchment and bake in the still-hot oven for around 2-3 minutes until fragrant and toasted. Remove from the oven and leave to cool before chopping half of them fairly finely and leaving some nuts whole. Spray with edible lustre spray.
To assemble, dollop a spoonful of frosting on top of each cupcake and tease around the edges using a rounded palette knife. To create a swirl, hold the cupcake in your left hand and turn it counter-clockwise as you run the knife across the top, pressing downward, in the opposite direction. It doesn't have to look too neat, the idea is to create some texture for the lustre spray to accentuate. Sprinkle over the chopped and whole hazelnuts and give each cupcake a dusting of shimmer with the gold lustre spray. Serve with prosecco and a fork if you’re feeling fancy or a cup of black coffee and your fingers if you’re not.
Recipe by Victoria Sponge Pease Pudding at http://victoriaspongepeasepudding.com/baking/nutella-brownie-cupcakes-with-salted-chocolate-hazelnut-buttercream/