To make the pastry, place the flour in a food processor with the icing sugar, pinch of salt and butter. Blend briefly until you have achieved a breadcrumb texture. Put the egg yolks in a small jug with the water and vanilla extract. Turn back on the machine and slowly pour in the liquid through the feeder tube. Be careful not to over blend or the pastry will become tough.
Turn the pastry out on to a lightly floured board and knead lightly until the pastry just comes together. Wrap in cling film and leave to rest in the fridge for about 20 minutes before using.
Preheat the oven to 180°C (350F), Gas mark 4. Cut the rested pastry in half and roll out each one into a large enough piece to line a rectangular loose-based tart tin that are approximately 30cm x 10cm, allowing any excess pastry to overlap the edges so that you get nice high sides on the finished tart. Repeat so you have two lined tart tins and lightly prick the bottoms with a fork. Line with cling film and then fill with baking beans or dried pulses or rice, then close over the cling film to enclose.
Bake blind for 15-20 minutes the sides are just until cooked through and beginning to catch colour. Remove the cling film and baking beans and return the tarts to the oven for another 10 minutes the bottoms of the pastry cases and lightly golden.
Meanwhile, make the frangipane. Beat the butter and sugar until creamed. Add the flour and almonds and stir until well combined. Add one egg at a time, making sure it is completely beaten in before adding in the next. This can be done in a food processor or with a wooden spoon.
Divide the frangipane between the cooked pastry cases so that it comes about half the way up the sides of the tins and then arrange the blackberries in neat lines on top. Return to the oven for another 30 minutes or so until cooked through and golden brown.
To make the blackberry puree, put the blackberries and caster sugar in a food processor and blend to a puree. Pass through a fine sieve into a jug. Cover with cling film and set aside until needed.
Heat the apricot jam in a small pan and pass through a sieve, then use to brush all over the warm tarts. Scatter over the almonds and then carefully trim down the sides and take out of the tins. Cut the ends off each tart and then slice into portions, then give each one a light dusting of icing sugar. Arrange the slices of blackberry and almond tart on warmed serving plates and decorate with the blackberries. Add a quenelle of crème fraiche to each one and then drizzle around a little of the blackberry puree to serve.