Preheat the oven to 130°C/ 250°F/Gas mark 1/2. Put the pastry shell on a baking sheet.
In a bowl, mix together the golden syrup, treacle, slivered almonds, breadcrumbs, eggs and lemon zest. Spoon the mixture into the pastry case, and bake for about 1 hour.
Serve warm with clotted cream or double cream.