preheat oven: 200°C, fan 180°C, 400°F, Gas 6
1. Butter a 20cm (8") tart tin with a removable base.
2. Put the flour, butter, icing sugar and cocoa powder into a large bowl and mix until it resembles fine breadcrumbs. Add the egg yolk and water and mix until the pastry binds together. You can also make this pastry in a food processor.
3. Wrap the pastry in clingfilm or a clean plastic bag and refrigerate for 30 minutes.
4. Sift a little cocoa powder onto the surface where you will roll out the pastry, to stop it sticking. Roll the pastry into a circular shape large enough to line the base and sides of the tart tin. Gently ease the pastry into the tart tin, and if it has a fluted edge, lightly press the pastry into the flutes.
5. Line the pastry case with foil and fill with baking beans, bake the pastry case blind for 20 minutes. Then remove the beans and foil and bake for another 10 minutes until the pastry shell is crisp and slightly browned. Remove from oven and allow the pastry case to cool completely.
1. Whisk the cream until it forms stiff peaks, the more air you can get into it the lighter the dessert will be.
2. Melt the white chocolate gently (see how to melt chocolate). When the chocolate is melted remove from the heat and allow to cool, stirring occasionally, but do not allow the melted chocolate to start to set.
3. Spoon a little of the melted chocolate into the pastry case and spread to cover the base. This will help to keep the pastry from going soggy when the raspberries are added if they are very juicy.
4. Fold the rest of the melted chocolate into the whipped cream.
5. Place a layer of raspberries in the pastry base to completely cover it. Then spread the cream and chocolate mixture over the top of the raspberries. Heap the cream more in the centre so that the filling has a convex shape. With a spoon create a small shallow depression in the very centre of the cream. Pile a few raspberries in this depression.
6. Put the rest of the raspberries into a blender and purée. Tip the puréed raspberries into a sieve and push through into a bowl, leaving the raspberry seeds in the sieve. Cover the bowl with clingfilm and refrigerate.
7. Remove the dessert from the tart tin and refrigerate until required.
8. Just before serving dust the cream filling with cocoa powder, avoiding the raspberries in the centre. Serve slices drizzled with the raspberry purée.