1. To make the pastry, stir the flour and sugar together in a bowl. Add the butter and rub it with your fingertips until the mixture resembles coarse bread crumbs. Mix the egg yolk with 3 tbsp cold water. Add the egg and process until the pastry draws together into a ball. Wrap and chill for 30 minutes.

2. On a floured surface, roll the dough into a 1/8 in (3mm) round circle and use to line six 4in (10cm) tart pans with removable bottoms. Prick all over. Chill for 30 minutes.

3. Preheat the oven to 400°F (200°C). Line the dough with wax paper and fill with baking beans. Bake for 10 minutes. Remove the paper and beans and bake for 10 minutes more, until the crust is golden and crisp.

4. Combine the white chocolate and ½ cup of the mascarpone in a heatproof bowl. Place over a saucepan of barely simmering water and stir until melted. Remove from the heat. Add the remaining mascarpone and whisk briskly until smooth, then whisk in the cream.

5. Spread in the tart shells. Refrigerate for 3 hours, until softly set. Mound the berries on the tart. Garnish with mint leaves, sift with confectioner's sugar, and serve chilled.