Make the sweet pastry. Place the flour in a bowl and rub in the butter until the mixture resembles crumbs. Stir in the sugar, pinch salt and egg yolks to form a dough.
Heat the oven to 160 c / Gas 2 1/2.
On a floured work surface, roll out the pastry to a thickness of about 5mm.
Line a 20cm flan ring or flan tin with a detachable base with the pastry. Cut off the excess pastry but leave about a 1cm rim (this will help to counteract the pastry shrinking when it is cooked in the oven). Keep off cuts of pastry for later by wrapping them in a piece of cling-film/plastic-wrap.
Scrunch up a piece of greaseproof paper and line the inside of the pastry, then fill the greaseproof paper with baking beans or rice, making sure they are into the corners, and put it into the oven for 20 minutes.
While the pastry is baking, put the golden syrup and treacle into a pan over a medium-low heat and warm it for about 3 minutes, until they have become runny and easily pourable.
Add all of the rest of the ingredients for the filling to the syrup and stir them in.
When the pastry has baked, remove it from the oven, take out the greaseproof paper containing the baking beans and allow it to rest until it is cool enough to handle.
Optionally, neaten the pastry crust by taking a sharp, serrated knife and trimming off the excess pastry until it is level with the rim of the flan ring or tin. Remove any crumbs from inside the pastry case and then pour in the filling mixture.
To make a lattice, roll out the raw pastry saved earlier and cut it into strips longer than the tart. Then lay the strips in a lattice pattern over the filled pastry case.
Using a pair of scissors, trim off the excess pastry hanging over the edge of the tart.
Put the tart back into the oven for 10 minutes.
Remove the tart from the oven and allow it to rest for 10 minutes before removing it from the flan ring or tin.