Preheat the oven to 180ºC and line and grease a 23cm springform tin.
Mix the flour and raising agents into a bowl and set aside.
Put the softened butter into the bowl of a freestanding mixer and beat until smooth. Add the sugar and cream together. Or use a stick blender or, indeed, a wooden spoon and elbow grease!
Next add the peeled bananas, broken into chunks and mix till incorporated, then add the vanilla. Note - the mixture will look like a curdled mess, but don't panic.
Now add the eggs, one by one, alternating with the dry ingredients, mixing all the while, until everything is used up and you have a finished batter.
Pour this into your prepared Springform tin and bake for around 50 minutes - but do start checking at 40 minutes. When the cake is done, a cake tester will come out more or less clean.
Leave to cool before unmoulding the cake.
Combine the rum, water, golden or corn syrup and sugar in a small saucepan, stirring to dissolve before putting over a low heat. Don't stir once it's on the heat. Let it come to the boil and then take it off the heat.
Add the finely chopped chocolate to the pan, swirling it around so that it is covered by the hot liquid. Leave to melt for a few minutes, then whisk to combine; it will quickly thicken and become smooth and shiny.
Straightaway, pour over the cooled cake, letting it drip down the sides, using a spatula to help ease it over the top as needed, and then immediately cover, as sparsely or as generously as you like, with your chosen sprinkles - or you can leave the gleaming chocolate surface as it is.