Set the oven to 180°C / 350°F / Gas 4. Mix flour, butter, and sugar together until it resembles breadcrumbs. Add the egg yolk and a little water until the dough binds together. Chill for an hour. Roll out the pastry and line a 20cm fluted flan tin. Prick the base and chill for a further 20 minutes.
Bake blind for 20 minutes until it is a pale, golden colour. Remove from oven and brush the inside of the case with egg white and bake for a further 2 minutes. Remove from oven and cool slightly.
Cream the butter and sugar together and gradually add the eggs and egg yolk. Fold in the ground almonds and lemon zest. Spread the pastry case evenly with the raspberry jam and then cover with the almond mixture. Bake for 20 minutes. Remove from oven and scatter with flaked almonds. Continue to bake for a further 15-20 minutes until golden and set. Remove from oven and place on cooling tray. When cool, remove from flan tin and dust with icing sugar.