Preheat the oven to 180°C. Line the bases of 3 x 20 cm cake tins with bake paper and grease the sides with butter.

Stir the cocoa powder, coffee and brown sugar in a bowl and pour over the boiling water. Whisk to mix and set aside.

Cream the butter and caster sugar together until pale and fluffy and then add the vanilla extract.

Add the eggs one at a time, beating well after each addition.

Slowly add the flour, bicarb and baking powder. Pour in the cocoa/coffee mixture and beat until just combined.

Divide the batter evenly amongst the 3 cake tins.

Bake in the oven for 20-25 minutes or until a skewer comes out clean.

Allow the cakes to cool slightly in their tins before turning out onto a tray to cool completely.

Place the softened butter and icing sugar in a large mixing bowl and beat until smooth.

Add the slightly cooled chocolate and continue beating until combined.

Add the Nutella and beat on medium-high speed until the buttercream is light and fluffy.

Using an offset spatula, spread half the Nutella on top of the first cake layer.

Place the second cake on top and spread the remaining Nutella over it (don't go down the sides).

Place the third cake on top and gently press down to sandwich the 3 layers together.

Dollop 2/3 of the Nutella buttercream on top of the cake, and using the offset spatula, begin to smooth the buttercream out across the top and over the sides of the cake.

Use the remainder of the buttercream to cover the sides of the cake (remember it doesn't have to be too neat as you will be covering the sides with hazelnuts!)

Chop the hazelnuts as finely as you want. Gently press them to the sides of the cake, dusting away excess nuts that fall off.

Decorate with Ferrero Rocher chocolates.