For the pastry, place the flour, cocoa powder, sugar and salt into a food processor and pulse to mix together. Add the butter, cut into small pieces, and pulse again until the mixture resembles breadcrumbs.

Add the egg and run the processor for 20-30 seconds until the mixture comes together to form a dough - you will hear, as well as see this. You may need to add a tablespoon of ice cold water if the pastry is very dry and not clumping together.

Form the pastry into a long tube shaped roll, slice off coin sized discs and use these to line a 26cm loose bottomed tart tin, pressing gently, but firmly to seal the joins. Leave a small overhang to allow for any pastry shrinkage.

If you are confident with pastry, you can go ahead and roll the pastry out, either on a floured surface or between two sheets of baking paper to fit the tin.

Prick the pastry all over with a fork, then cover the lined tin with cling film and chill for at least 30 minutes.

Preheat the oven to 200°C/400°F/Gas 6. Take the tart tin out of the fridge and remove the cling film. Crumple up a nice big piece of baking paper, then smooth it out and place it over the pastry. Cover this with a large square of tin foil, pushing this into the corners of the inside of the tin. Weigh down with baking weights or uncooked rice, then bake in the preheated oven for 15 minutes. Remove the paper/tin foil lining and rice and return to the oven for five minutes. When cooked, remove from the oven, and if you like, use a small, sharp knife to trim and tidy the edges while the pastry is still warm (you can leave them too for a more rustic effect!) and set aside.

Meanwhile, for the filling, bring the cream, butter and vanilla extract to just under a simmer in a saucepan - you want to see small bubbles around the rim of the pan but it should not boil.

Break the chocolate into pieces and place into a large bowl. Pour over the cream mixture allow to sit for 5 minutes, then whisk slowly until the chocolate has melted and the mixture is smooth, dark and glossy.

Pour the chocolate mixture carefully and slowly into the tart case, gently shake the tin to pop any large air bubbles, and use a skewer or toothpick to pop any smaller ones - this will give you a nice, smooth surface. Place in the fridge to set for at least two hours.

Top with fruit of your choice, and slice with a sharp knife, dipped in hot water between cuts. Serve thin slices, with whipped cream.