Start by making the pastry. Put the flour and cold cubed butter into a large bowl and combine using your fingers until crumbly. Add Lyle's Golden Syrup and 1 tbsp of cold water and keep using your hands to bring the dough together. If it's still dry and crumbly, add another tbsp of cold water.
Shape into a ball and wrap into a cling film. Refrigerate for 30-60 minutes.
While the pastry is cooling down, prepare the filling.
Add the egg yolks, Lyle's Golden Syrup, sugar, and cornflour into a large bowl and whisk until pale and smooth. Heat the milk in a saucepan until almost boiling. Remove from heat and slowly pour one-third of milk into the egg yolk mixture whisking continuously. Now pour the remaining milk into the egg yolk mixture and whisk until combined.
Pour back into the saucepan and gently heat stirring continuously until thickened. Remove from heat, whisk in vanilla extract, then transfer into a clean bowl and cover with cling film. Let cool down to room temperature.
Now remove the pastry from the fridge and roll out into a circle a bit larger than the 23cm baking tin. Place the pastry into a greased baking tin, press down, and cut the excess.
Prick with the fork and put back into the fridge for 30 minutes before baking.
Preheat the oven to 190C (170C fan).
Line the chilled pastry with baking paper, fill with baking beans or rice, and bake for 20 minutes. Remove the baking beans and continue baking for additional 15 minutes. Let cool down completely.
To assemble, spread the jam over the cooled base, top with the custard filling (stir the custard before to make sure there are no lumps) and sprinkle with coconut. Add a glace cherry for a retro touch if desired.