Prepare pastry or crumb shell.
Combine cornflour and cold water to a smooth paste.
Melt butter, add brown sugar. Cook slowly until it caramelizes, stirring all the time, a whisk is best for this.
Add mixed warm water, salt, and golden syrup. Boil until all sugar has dissolved.
Add cornflour mixture, stir until thickened.
Combine some of the above mixture with the egg yolks (¼ a cup or so) whisk. Then add back to the pot with the remaining mix.
Add vanilla and rum. Fold in sliced bananas. Pour into the pastry shell and cover with whipped cream, sifted cocoa and extra banana slices.