Rub the butter into the flour until it resembles breadcrumbs. Add the egg, sugar and lemon zest and knead to a pastry dough. Wrap in cling film and chill in the fridge for 1 hour.
For the filling:
Meanwhile prepare the filling. In a saucepan, combine the water, sugar and vanilla pod. Bring to the boil and cook for 10 to 15 minutes, until the mixture has the consistency of syrup.
Add gooseberries and simmer for another 5 to 10 minutes. The gooseberries should be soft, but not breaking apart. Strain the mixture, reserving the syrup. Pour syrup back into the saucepan and continue simmering, until thick. Set aside.
Preheat oven to 200 C / Gas 6. Grease a 25-26cm springform tin or a loose-bottomed tart tin.
Roll out 2/3 of the pastry and line the bottom and 2cm up the sides of the tin. Prick the pastry all over with a fork.
Prebake the pastry case for 20 minutes in the preheated oven.
Roll out the remaining pastry and cut into long and thin strips. Spread the gooseberries evenly over the prebaked pastry case. Arrange half of the dough strips on top going one direction and top them with the other half going the other direction. Brush the lattice with the beaten egg.
Bake for 30 minutes in the preheated oven.
Take the pie out of the oven, remove the springform ring and place on a cooling rack. Drizzle with the syrup and let cool.
Choose gooseberries that are not too ripe, the recipe works best if the berries are ripe, but firm.