400 g shortcrust pastry
24 cm flan tin
20g unsalted butter
3 shallots, finely diced
2 egg yolks
110g crème fraîche
40g parmesan, grated
120g feta, crumbled into biggish pieces
Salt and freshly ground black pepper
Heat the oven to 180C (conventional)/160C fan/gas mark 4.
Roll out the pastry evenly, to the thickness of a pound coin, and use it to line the tin. Chill for a minimum of 30 minutes.
Place the tart tin on a baking sheet, prick the pastry base all over with a fork and line with baking parchment or foil weighted down with baking beans (or uncooked rice or pulses). Bake for 15 minutes, remove from the oven and take out and remove the liner and beans/rice. Return to the oven for 12 minutes, until the base is cooked and golden.
While the pastry case is cooking, warm the butter over a medium-low heat and sauté the shallots until soft (about 10 minutes).
Put the watercress in a food processor with the eggs, egg yolks and crème fraîche, and pulse to a green purée. Stir in the parmesan and feta and the softened shallots, and season. Tip the mixture into the tart shell and bake for 30 minutes until golden.