Mascarpone Tart with Blueberries

Method

1. To make the pastry, put the flour, sugar, lemon zest, sour cream and a large pinch of salt in a small processor fitted with the plastic blade. Whizz for 8–10 seconds, or until combined. With the motor running, gradually add the olive oil, stopping once the mixture resembles wet breadcrumbs. Remove from the processor and knead briefly to form a smooth ball. Cover with plastic wrap and chill for 30 minutes.
2. Preheat the oven to 190°C (375°F/Gas 5). Grease an 18 cm (7 inch) loosebased tart tin. Roll out the pastry between two sheets of baking paper to a circle large enough to fit the prepared tin. Use the pastry to line the tin, then trim the edges. Line the pastry with a piece of crumpled baking paper and pour in some baking beads or uncooked rice. Bake for 12 minutes, then remove the paper and beads and return to the oven for another 8 minutes, or until golden. Set aside to cool for 10 minutes.
3. Meanwhile, put the mascarpone, sour cream and sugar in the cleaned processor. Whizz for 15–20 seconds, or until smooth. Add the lemon zest, vanilla, cornflour and egg yolks and whizz for 12–15 seconds, or until combined.
4. Transfer the mixture to a metal bowl over a saucepan of simmering water. Cook, stirring often, for 30 minutes, or until the mixture is thickened and holds its shape. Spoon into the pastry case and level the surface. Sprinkle the blueberries over the surface, pressing them in gently. Set aside to cool completely. Serve dusted with icing sugar.