For the sweet pastry, in a bowl, rub together the flour and butter using your fingertips, until the mixture resembles breadcrumbs.
Add the icing sugar, egg yolks and cold water and mix until the mixture comes together as a dough.
Wrap the dough in cling film, then chill in the fridge for two hours, to rest.
Grease a 23cm/9½in loose-bottomed tart case with melted butter, then dust with flour, gently knocking out any excess.
Meanwhile, line a baking tray with greaseproof paper and place the prepared tart case on top.
Once the pastry has rested, discard the cling film and roll the pastry out onto a lightly floured work surface to a 4-5mm thickness.
Lift the rolled pastry by rolling it loosely around the rolling pin, then lower it into the prepared tart case and press into the tart case to mould it to the sides and bottom. Trim off any excess pastry using a sharp knife. Chill the tart case in the fridge for a further 30 minutes.
Preheat the oven to 200C/400F/Gas 6.
When the tart case has rested, remove it from the fridge and prick the base several times using a fork.
Line the base and sides of the tart case with greaseproof paper, then fill it with baking beans. Transfer to the oven and bake for 30-35 minutes, or until crisp and pale golden-brown. Discard the greaseproof paper and baking beans.
For the filling, blend the bread in a food processor until it has formed breadcrumbs. Set aside.
Heat the golden syrup and butter in a pan over a low to medium heat until the syrup and the butter has melted. Set aside to cool slightly.
In a separate bowl, whisk together the egg and cream until well combined. Pour in the syrup and butter mixture and stir to combine.
Stir in the breadcrumbs, lemon zest and salt until well combined.
Pour the filling mixture into the cooked pastry case, then return the tart to the oven and cook for a further 40-45 minutes, or until the filling is dark golden-brown.
Remove from the oven and set aside for 15 minutes before serving to allow to cool slightly. Serve warm, with clotted cream or whipped cream.