For the pastry: Mix the flour, caster sugar and salt together into a bowl. Add the diced butter, rubbing in with your hands until it resembles breadcrumbs. Add the water 1tbsp at a time until the dough starts to come together. Turn out onto a lightly floured worktop, and knead until it comes together to form a uniform dough. Don't handle it too much. Wrap the dough in clingfilm and put in the fridge for 30 minutes.
Once chilled, roll the pastry out on a floured work surface into a rectangle about 2-3mm thick. Line the tin with the pastry and then pop back in the fridge for 30 minutes until firm. Then pre-heat the oven to 180C/160C Fan/Gas Mark 4.
Once the pastry is firm, line it with baking paper and fill with baking beans. Then bake for 20 minutes.
For the filling: Whilst the pastry is baking, place the golden syrup in a pan and gently warm. In a separate bowl mix the cream, eggs and grated lemon zest, then add the warm golden syrup (make sure its not too hot or it will cook the eggs).
In a separate bowl, mix the breadcrumbs and ground almonds together and then make a well in the centre. Pour the golden syrup mixture into the well and mix until smooth.
Once the pastry is baked, remove from the oven and remove the beans and baking paper. Then return to the oven and bake for another 5 minutes until the pastry is dry.
Fill the baked pastry case with the treacle mixture and then bake for 15-20 minutes or until the filling is just set. Serve warm.