Creamy onion tart

Method

1. Put all the pastry ingredients into the bowl of a food processor, then whizz briefly until the mixture resembles fine breadcrumbs. Remove the lid, add 2 tbsp cold water, then whizz again until everything starts to stick together. Tip the pastry onto a lightly floured surface and knead briefly until smooth. Roll out thinly, then use to line a lightly greased 23cm diameter, 3-4cm deep loose-bottomed flan tin. Prick the base with a fork, then transfer to the fridge to chill for 20 minutes.
2. Meanwhile, make the filling. Melt the goose fat or butter in a large, shallow pan with a lid, then add the onions and cook gently, covered, for 10 minutes. Remove the lid and raise the heat slightly, then cook for another 20 minutes, stirring often, until very soft and just beginning to colour. Season lightly, then transfer to a large mixing bowl and set aside.
3. Put a heavy-duty baking sheet into the oven and preheat to 200°C/fan 180°C/gas 6. Line the chilled pastry case with a crumpled sheet of baking paper, then a thin layer of baking beans or rice. Slide the flan tin onto the hot baking sheet and bake for 15-20 minutes until the pastry is biscuit-coloured around the edges. Remove the paper and beans/ricethen return to the oven for 5-7 minutes until the base and sides are crisp and golden. Remove from the oven and set aside, then lower the heat to 190°C/fan170°C/gas 5.
4. In a mixing bowl, beat the eggs with the nutmeg and cream or crème fraîche, season to taste, then stir into the bowl of cooled onions. Pour the mixture into the pastry case, using a spoon to evenly distribute the onions, then slide the flan tin back onto the hot baking sheet and cook for 25-30 minutes until the filling is set and lightly golden. Leave to cool slightly before removing from the tin and cutting into slices to serve.