Cheese and onion quiche

Method

1. Heat the oven to 180°C fan/gas 6. For the pastry, put the flour, salt and butter in a food processor, then pulse to a breadcrumb consistency. In a small bowl, beat the egg with 2 tbsp of the water. Add to the flour and whizz briefly to bring the pastry together, adding the remaining tbsp of water if needed. (If you don’t have a food processor, rub the butter into the flour/salt with your fingers, then add the yolk/water and mix with a dinner knife.) Turn out onto a floured work surface, then bring together in a ball (see Make Ahead). Roll out the pastry to a 30cm disk and use to line the tart tin. Leave a little pastry overhang (don’t trim), then chill for 30 minutes.
2. Prick the chilled pastry base all over with a fork, then line with a piece of baking paper (scrunch it up, then flatten it out again so it fits the shape of the case more easily). Fill with ceramic baking beans or uncooked rice, then blind bake for 20 minutes. Remove the paper and beans/rice and bake for 8-10 minutes more until golden and the pastry feels sandy. Remove from the oven, set on a baking tray and trim the pastry overhang with a serrated knife. Turn down the oven to 150ºC fan/gas 3½.
3. For the filling, whisk the cream, milk and eggs together in a large bowl. Add the grated cheese, caramelised onions and mustard with a pinch of salt, then stir to combine. Pour the filling into the hot tart shell (see Know-how), then return, on the baking tray, to the oven for 45 minutes or until set with a slight wobble in the centre. Cool, then slice and serve.