200g hazelnuts, ideally with their skins on
100g dark chocolate
1 tsp baking powder
2tsp instant coffee, mixed with 6 tsp of boiling water
5 eggs, separated
75g caster sugar (granulated sugar for my US friends)
pinch of salt
Chocolate topping ingredients
90g dark chocolate
Place the hazelnuts, chocolate and baking powder in a food processor and blitz until you have coarse crumbs. Add the coffee and butter then blitz again until mixed.
In a large bowl, beat the egg yolks and the sugar together until light and fluffy. Add the coffee and the hazelnut mixture to the egg/sugar mixture and beat by hand until combined. Note, what you'll end up with will be a fairly firm paste like texture.
Using an electric mixer, whisk the egg whites and the pinch of salt together until stiff. Then add one-third of the egg whites to the other ingredients and stir well to combine. This first third will help remove the paste like texture from the batter. Add the remaining egg whites in two batches, folding in carefully to retain as much air in the mixture as possible.
Pour the mixture into the cake tin and bake at 170°c, (340f), for about 45 minutes. Leave to cool for 5 minutes in the tin and then turn out onto a wire rack to cool completely.
To make the chocolate topping, fill a saucepan about 1/4 full with water and simmer over a medium heat. Place a mixing bowl on top of the saucepan and add the chocolate. Once the chocolate melts add the butter and stir until combined. Take the mixing bowl off the saucepan and leave to cool for 15 minutes.
Drizzle your chocolate over the top of your cooled cake.