On a lightly-floured surface, roll out the pastry to 1⁄8in (3–4mm) thick and use it to line a 10-in (28-cm) loose-bottomed tart tin. Cut any excess pastry from the tin. Chill the pastry in the tin for about 20 minutes.
Preheat the oven to 400ºF?200ºC.
When the pastry has chilled, line it with parchment paper and baking beans and bake for 15 minutes. Remove the baking paper and beans and return to the oven for a further 5 minutes or until lightly golden.
Meanwhile prepare the filling. In a large heavy-based saucepan heat the oil and butter. Add the onion, fennel and leeks and sweat until cooked and tender but not browned, about 6–8 minutes. Stir in the garlic and cookfor a further minute then remove from the heat.
In a separate bowl combine the mascarpone (or sour cream), cream and eggs and lightly beat together. Add the cream mixture, Parmesan cheese and basil
leaves to the leek mixture and stir to combine. Season generously with salt
and pepper. Reduce the oven temperature to 350ºF/180ºC. Pour the filling mixture into the warm pastry case and bake in the oven for 25–35 minutes or until set and golden on top.
Serve warm or at room temperature.
- Mascarpone is a thick, rich, Italian cheese. Sour cream can be substituted.
- Baking beans are just raw, uncooked, dried beans. They keep the pastry from puffing up and cracking while baking. They can be reused for baking again and again. Artificial baking beans are also available in cooking stores.