- Make the pastry first (skip to step 5 if using store bought pastry). Put the flour, sugar and salt in a food processor and blitz briefly to combine (or sieve into a bowl).
- Add the butter and blitz (or rub in with your fingertips) until the mixture resembles breadcrumbs.
- Add the egg yolk, and enough milk or water to bring it together into large clumps.
- Tip out on to a lightly floured surface and knead gently into a ball.Wrap in clingfilm and chill for 30 minutes.
- Heat the oven to 190C/375F/gas mark 5 and put a baking sheet inside. Roll out the pastry to fit a 24cm tart tin.
- Line the tin with the pastry, leaving the excess hanging over the edge. Prick all over with a fork and chill for 10 minutes more.
- Line the pastry with greaseproof paper or foil, making sure the edges are covered. Fill with baking beans or uncooked lentils or rice, and bake blind for 15 minutes.
- Remove the beans and paper, and cook for another five minutes, or until the pastry looks cooked but not browned.
- Leave to cool, then trim off the rough edges. Reduce the oven to 180C/350F/gas mark 4.
- Remove any tough stalks from the sorrel. Wash the leaves, dry thoroughly and shred finely. Heat half the butter in a large frying pan over a medium-low heat.
- Add half the sorrel and cook for a few minutes, stirring often, until collapsed and drastically reduced in volume.
- Transfer to a colander to cool. Repeat with the remaining sorrel. When cool, squeeze out the excess moisture with your hands.
- In a wide bowl, whisk together the eggs, egg yolks, cream and milk. Sift in the icing sugar, whisk to dissolve, then stir in the raisins and wilted sorrel.
- Pour carefully into the prepared pastry case, using a fork to distribute the sorrel and raisins evenly.
- Bake for about 40 minutes, or until set and just golden. Leave to cool, and serve warm or at room temperature.
