Preheat the oven to 200°C/400°F/Gas Mark 6
First make the pastry – sift together the flour, cocoa, salt and icing sugar. Rub in the cold butter using a food processor or your fingertips until the mixture resembles fine breadcrumbs. Mix the egg yolk with the cold water, and add to the mixture to bring together. Shape the pastry into a flat disc and chill in the fridge for half an hour. Roll out the pastry and use to line a 23cm loose bottomed tart tin. Prick the base with a fork and chill for half an hour or until the pastry is solid.
Line the pastry case with a circle of grease-proof paper, fill with baking beans and bake blind for 15 minutes. Remove the beans and bake for a further 2-3 minutes until the pastry is dry and biscuity. Remove the pastry case from the oven and leave to cool. Turn the oven down to 190˚C/375˚F/Gas Mark 5.
When cool, spread the jam over the bottom of the pastry case, and scatter over the raspberries. Whisk together the eggs, sugar, almond essence and vanilla seeds until pale. Add the melted butter and whisk until well combined. Finally fold in the ground almonds. Spoon this mixture over the raspberries, and bake the tart for 20 minutes.
Sprinkle the flaked almonds over the top, and bake for a further 10 minutes, until the filling is set and golden brown. Dust with icing sugar and serve warm, with cold cream or icecream.