Blackberry Cottage Tart

In the orchard of the cottage where we spend our summer holidays grow the most succulent blackberries I have ever tasted. If you are lucky enough to have some first-class blackberries (remember that blackberries vary enormously in flavour, so taste them first) within easy reach, this tart, with its crisp, lemon pastry and soured cream filling, could become as much of a favourite with you as it is with us. Alternatively, you could make it with raspberries or strawberries.