Start by making the pastry, if making your own. Add the butter to the flour and rub with your fingertips until the texture resembles breadcrumbs (alternatively, this can be done in a food processor). At this stage, add in the water until a dough forms. Wrap in clingfilm and chill in the fridge for 15 minutes.
Preheat the oven to 180C Fan/200C/400F/Gas Mark 6. Lightly grease a 23cm loose bottomed tart tin with oil/butter.
Roll the pastry to about 1-2cm thick, enough to cover the tin. Press to the edges and cut off any excess around the edges.
To do the blind bake: Place a circle of greaseproof paper on top of the pastry – enough to go up the sides. Add in baking beans/uncooked rice so that the base is entirely covered and weighed down.
Bake for 10 minutes, before removing the paper/beans/rice, then bake for a further 5-10 minutes, until the pastry is just cooked and lightly golden.
While the pastry is baking, add the hazelnuts to a lined baking tray and toast for 10 minutes. Remove and set aside to cool on a wire rack.
Once the pastry is baked and cooled, make the chocolate filling. Do this by chopping all the chocolate really fine and placing into a heatproof bowl.
In a small saucepan, heat the cream and butter together on a very low heat, until the butter has melted and bubbles are just forming at the edges (very close to boiling but not quite). Pour this over the chocolate and let it sit for two minutes before stirring together – it will become a gorgeous shiny chocolate colour. Pour this into the pastry case and spread evenly.
Shake your pan of hazelnuts about to remove the skins (you can also use your hands but they should easily fall off) and place into a small bowl. Line a large baking tray ready for the next step.
To make the praline: add the sugar and 6 tbsp water to a medium saucepan over a medium heat. Keep an eye on it but do not touch/stir – let it sit on this heat for 10-15 minutes, until it turns an amber colour. At this point, swirl it very gently, then tip in the hazelnuts and butter. Stir together and pour onto the lined tray. Let cool.
Once cool, add half of this sugary/caramel hazelnut mix to a food processor (or smash with a rolling pin) to create a dust. Sprinkle this dust in a circle over the tart. Break up the remaining praline into big chunks and place at various points on the tart.
Slice and serve. Whipped cream makes for good pairing, but is not at all necessary. Enjoy!