WHAT YOU NEED

For the hazelnut buttercream
285g unsalted butter, softened
1⁄4 tsp sea salt
450g icing sugar, sifted
4 tbsp Hazelnut Butter
11⁄2 tbsp milk

For the hazelnut sponge
115g self-raising flour
10g cocoa powder
a pinch of sea salt
1⁄4 tsp bicarbonate of soda
115g caster sugar
10g soft light brown sugar
125g unsalted butter, softened
2 eggs
11⁄2 tbsp milk
25g Hazelnut Butter

For the filling
100ml double cream
1 tsp icing sugar, sifted
1 tbsp Hazelnut Butter

For the hazelnut sponge
Preheat your oven to 190°C (170°C fan) and line a 12-hole cupcake tin with paper cases.
Sift the flour, cocoa, salt, bicarb and sugars into the bowl of a stand mixer fitted with the paddle attachment, or a large bowl.
Add the butter and eggs, and beat on a medium–high speed for 30 seconds until well combined. Add the milk and hazelnut butter and beat for 30 seconds, stopping to scrape the sides and bottom halfway through, until you have a smooth batter.
Distribute the batter evenly among the paper cases until they are three-quarters full.
Bake for 18–20 minutes until the tops spring back when gently pressed.
Leave to cool.

For the hazelnut buttercream
In the bowl of a stand mixer fitted with the paddle attachment or a medium mixing bowl, beat the butter and salt together on a high speed for at least 5 minutes until the butter has turned a very pale yellow and the texture is smooth and whippy.
Add half of the icing sugar and bring together on a slow speed to avoid plumes of sugar jumping out of the bowl, then beat vigorously for a few minutes before repeating with the remaining icing sugar.
Beat until you have a pale, almost white, fluffy mixture.
Beat in the vanilla, then the milk, a little at a time. Depending on the softness of your butter and the temperature of your kitchen, you might not need to add all of the milk, or you may even need a bit more. You’re looking for a smooth, whippy buttercream that has a spreadable consistency and holds its shape.

For the filling
In a bowl, whip the cream, sugar and hazelnut butter with a balloon whisk until medium-soft peaks are forming, then put the mixture into a piping bag.

To finish
Using an apple corer, remove the centre of each cupcake, then fill the holes with the cream filling. Take care not to overfill.
Put your buttercream into a piping bag fitted with a large round nozzle and squeeze a neat blob of buttercream on top of each cupcake.
Put the iced cupcakes in the fridge for 15 minutes while you melt the chocolate for the topping in a bain-marie or in the microwave in short bursts.
Add the melted cocoa butter and stir to combine, then leave to cool for 5 minutes.
Dip the chilled iced cupcake tops into the chocolate, allowing the excess to dribble back into the bowl. Sprinkle with hazelnuts to finish.