Preheat the oven to 200°C (180°C fan assisted oven, 400°F, gas mark 6). Divide the pastry into 6 equal portions and roll out each piece on a lightly floured surface to fit six, 12cm (5inch) round flan tins. Trim and line with baking parchment.
Half-fill the tarts with ceramic baking beans or raw rice and bake for 15 minutes. Carefully remove the parchment and beans, prick with a fork and return to the oven for a further 5 minutes until lightly golden and firm. Leave to cool for 10 minutes before removing from the tins.
Meanwhile, whisk the egg yolks and sugar together until pale and thick. Whisk in the flour, cornflour and 60ml (4 tbsp) of the milk to make a smooth paste then stir in the remaining milk.
Transfer to a saucepan and stir over a low heat until boiling and cook for 2 minutes until thick. Remove from the heat, add the Natural Vanilla Extract, cover the surface with a sheet of buttered greaseproof paper and leave to cool completely.
For the glaze, place the Ground Arrowroot in a small saucepan and blend with a little of the fruit juice to make a paste. Add remaining juice and gently bring to the boil, stirring until clear and thickened. Leave to cool for 20 minutes.
To assemble, spread the custard into each pastry case. Arrange the berries on top and carefully spoon over the prepared Ground Arrowroot glaze to coat the fruit. Chill for an hour before serving.