For the pastry, rub the butter into the flour until the mixture resembles breadcrumbs. Gradually add the beaten egg and mix together to make a dough. You may need to add a little cold water.
Wrap the dough in cling film and place in the fridge for at least 30 minutes. If you are making five tarts, divide the mixture into five portions of equal weight and wrap them separately.
Preheat the oven to 180C/350F/Gas 4. Lightly grease five 25cm/10in loose-bottomed tart tins, or two 40cm x 30cm/16in x 12in baking trays.
On a lightly floured surface, roll out the pastry and use to line the tart cases or the baking trays.
Cover the pastry case with cling film and place in the fridge to rest for 15 minutes.
Remove the pastry from the fridge and remove the cling film. Line the pastry cases with greaseproof paper and fill with baking beans.
Transfer to the oven and blind bake for 10-15 minutes.
Remove the pastry cases from the oven and remove the greaseproof paper and baking beans. Return to the oven for a further 3-5 minutes.
Remove the pastry cases from the oven and lower the oven temperature to 140C/275F/Gas 1.
For the filling, place the golden syrup, breadcrumbs, beaten eggs and lemon juice and zest into a large bowl and mix well.
Pour the filling mixture into the pastry cases, transfer to the oven and bake for about 50 minutes or until golden-brown. Remove from the oven and allow to cool slightly.