Berry jam lattice tart

Method

1. Put the berries in a large heavy-based pan with the preserving sugar and lemon juice. Leave to macerate for 15-20 minutes, stirring now and then with a wooden spoon and gently squashing the berries. This will help the sugar dissolve and draw the juices out of the berries.
2. Meanwhile make the pastry. Whizz the flour, butter and a pinch of salt in a food processor until the mixture resembles fine breadcrumbs. Add the yolk with 4 tbsp ice-cold water, then pulse until the pastry comes together into a ball; add a little extra water if needed. (If you don’t have a food processor, rub together the flour and butter with your fingers in a bowl, then stir in the egg yolk and water with a wooden spoon.) Tip out the pastry onto a piece of cling film and shape into a disc. Wrap, then chill for 30-40 minutes until firm.
3. Put 2 small plates in the freezer, ready to test the set of the jam. Put the pan of macerated berries over a low heat and warm gently until all the sugar has dissolved. Increase the heat and vigorously boil until the jam reaches 105°C – depending on the size of your pan, this will take anything from 5 to 15 minutes. The jam should be visibly thicker.
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4. Remove the pan from the heat, then spoon a small blob of jam onto one of the cold plates from the freezer. After a few seconds, push your finger through the jam – if it wrinkles it has reached setting point. (If not, put the pan back on the heat and bubble for 1-2 minutes more.) Leave the pan off the heat for the jam to settle, then skim off any scum floating on the surface. Leave the jam to cool while you make the pie case.
5. On a floured surface, roll out two thirds of the pastry to a 30cm circle. Carefully roll the pastry around the dusted rolling pin, then unroll into the tart tin. The pastry will be quite crumbly but if it breaks, just patch it up. Use a small piece of pastry to push the pastry case into the edges of the tin, then trim away any excess, saving the offcuts for the lattice. Prick the base all over with a fork. Chill for 30 minutes (or for 10 in the freezer) and heat the oven to 200°C/180°C fan/gas 6.
6. Line the case with a large piece of baking paper/foil and fill with ceramic baking beans or rice. Bake for 20 minutes, then remove the beans/rice and paper/foil and bake for 5 minutes or until the pastry feels sandy. Leave to cool slightly.
7. Spoon the jam into the case, then roll out the rest of the pastry into a rectangle the thickness of a £1 coin. Slice the pastry into 3-4cm strips, re-rolling if necessary. Lay the strips in a lattice over the pie, with 3 strips going in one direction and 3 crossing them.
8. Sprinkle the tart with caster sugar, then bake for 25-30 minutes until the pastry is golden on top and the filling is warmed through. Leave the tart to cool to room temperature, then serve with cream or ice cream.