Place the double cream and sugar in a saucepan and heat until steaming (make sure it doesn’t boil as this will cause the ganache to split), then add the chocolate, stirring until melted. Once smooth, cover this and place in the fridge for at least 2 hours, until solid.
Meanwhile, make the pancake batter. Place the flour and sugar in a large bowl and create a well in the middle with a wooden spoon. Combine the beaten eggs with the beaten egg yolks and gradually add the eggs to the bowl, continuing to stir in the middle of the bowl. Once all the eggs have been added, add the milk and continue stirring until smooth. Add the oil, then cover and leave to rest in the fridge for at least 30 minutes.
Meanwhile, make the caramel hazelnut shards. Lay large sheets of foil or greaseproof paper on the floor underneath your work surface. Spear the sharp end of a long wooden skewer to each hazelnut. Get 10 pieces of sticky tape ready. Place the granulated sugar in a small saucepan over a medium heat until melted and a dark golden colour. Remove from the heat and swirl the pan to slightly cool the caramel until it has thickened slightly. Quickly dip the hazelnut into the caramel and place the skewer with the hazelnut dripping on to the foil on the floor, fastening the skewer to your work surface with a piece of tape. Repeat with the remaining hazelnuts – if the caramel starts to solidify, gently reheat it to the right consistency. Leave to firm up for at least 15 minutes, then cut off any long, thin trails of caramel. Carefully remove the hazelnuts from the skewers and lay them on a sheet of greaseproof paper.
Start making the pancakes. Place an 18cm non-stick frying pan over a medium heat and brush with sunflower oil, then put roughly ¾ of a ladleful of batter in and swirl the mixture so that it covers the base of the pan. Leave for 1-2 minutes until the top has completely set and the bottom side is golden. Loosen the edges with a spatula, flip over, and cook the other side for 20 seconds until lightly golden, then transfer to a sheet or plate lined with greaseproof paper. Continue until all the pancake batter is used up, placing a sheet of greaseproof paper between each pancake so they don’t stick to each other. You should end up with around 30 pancakes. Once cooled slightly, place in the fridge until cold.
Remove the ganache from the fridge and warm slightly over a pan of lightly simmering water so it slightly softens. Beat with an electric mixer on a high speed for 5 minutes until completely smooth and slightly lightened in colour. It should now be a spreadable consistency, but not too loose as this will prevent the finished cake from having a solid structure while layering it up.
Once the pancakes are cold, place one on a cake stand and spread over 1 tablespoon of ganache with a palate knife. Start by spreading the mixture around the edge of the pancakes, then work the mixture into the middle. Make sure you spread the ganache right to the edges of the cake. Continue this until all the pancakes and ganache is used up, leaving the top pancake bare.
Make the chocolate glaze. Place all the ingredients in a heatproof bowl over a pan of simmering water until melted, stirring regularly until completely smooth. Pour ¾ of this mixture over the top of the cake and, using a palate knife, bring to the edges so that it drips down the sides without completely covering them (you should still be able to see the edges of the pancakes). Use the remaining quarter to smooth over the top of the cake. Place this in the fridge for 15-20 minutes until the glaze has slightly firmed up, then place the caramel hazelnuts on top with the spikes sticking up.