Roll out the pastry on a lightly floured surface, then cut out 2 circles and use to line 2 x 10 cm (4 inch) tart tins, trimming off any excess. Prick the bases with a fork and line with baking paper and baking beans.
Place the tins on a baking sheet and bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 10 minutes. Remove the paper and beans and return to the oven for a further 5 minutes until the pastry is crisp and golden. Leave to cool.
Meanwhile, melt the white chocolate in a microwaveable bowl in a microwave on Medium, checking every 30 seconds until melted and smooth, taking care not to let it overheat.
Beat together the mascarpone and cream in a bowl until smooth, then beat in the melted chocolate. Spoon the mixture into the cases, then top with the fruit and some white chocolate shavings. Dust with icing sugar and serve.