Put the flour, icing sugar and cocoa in a food processer along with the cubed butter.

Pulse several times until the mixture resembles fine breadcrumbs.

Mix the egg yolk with the cold water and add gradually while continuing to pulse. The mixture will quickly form clumps.

Put a large piece pf plastic wrap on the worktop and tip the dough out onto it.

Use the wrap to push the dough into one clump and then flatten it out.

Wrap the dough and refrigerate for 15 minutes.

Take off the top layer of plastic and flip the pastry over and onto the tin. Use the plastic to gently push the pastry into the edges. Peel off the remaining plastic.

Fork the base of the pastry and chill for 20 minutes.

Preheat the oven to 200 C / 400 F / 180 FAN / Gas 6 and bake blind for 15 minutes. Remove the beans and paper and bake for a further 10 minutes.

Leave the pastry to cool in the tin.

Break up the chocolate into small pieces and place in a large bowl with the caster sugar.

Heat the cream to boiling point in a small saucepan.

Pour the cream over the chocolate and sugar and leave for about 3 minutes.

Stir until the mixture comes together and is smooth and one colour.

Leave to cool for about 20 minutes.

Pour the chocolate ganache over the pastry base.

Carefully push in the raspberries.

Chill for at least 2 hours before serving.