Preheat the oven to 180°C/fan 160°C/gas 4. To make the pastry, place the flour, sugar and butter in the food processor and pulse until it resembles breadcrumbs. Gradually add the egg yolks and process again until the pastry comes together.
If there’s time, leave the dough to rest in the fridge for 10 minutes before rolling out. Flour a clean work surface or put a piece of greaseproof paper on your work surface. Roll out the pastry dough using a floured rolling pin until it is about 3mm thick. Using the rolling pin to support the weight of the pastry, drape the pastry over a 22cm tart tin, pressing the pastry into the base and sides. The dough will be quite resilient, but work quickly. Cut a circle of greaseproof paper to fit the tart tin, place it inside on top of the pastry base and put some baking beans on top.
Blind bake the pastry base in the preheated oven for 25 minutes, then remove the baking beans and return the tart tin to the oven for a further 10 minutes. Take out of the oven and leave to cool, still in its tin.
Meanwhile, heat the cream in a medium-sized saucepan over a low heat. Just before it begins to boil, remove the pan from the heat and stir in the chocolate until it has all melted.
Once the tart case has cooled, trim any excess dough from around the edge, scatter the raspberries in the bottom and pour in the chocolate cream mixture. Leave to cool a little before chilling in the fridge for 30 minutes.
Place the crème fraîche in a small bowl, add the icing sugar, Frangelico and all but 1 tablespoon of the hazelnuts and stir to mix.
When you’re ready to serve the tart, a quick blast with a blow torch over the surface brings the cocoa butter out to give a great gloss. Slice the tart into thick wedges using a sharp knife that has been warmed under running hot water. This will ensure a smooth finish. Place each slice on a serving plate, with a spoonful of the hazelnut crème fraîche and a few extra raspberries.