Heat a pan and add the sugar along with a dash of water to the pan to caramelise. Swirl the pan over a medium heat until the caramel starts to turn a dark golden colour. Once golden remove from the heat and add a 100ml of double cream. Whisk in, being careful of the spitting caramel.
Once the cream is mixed in add 30g of cold cubed butter, cube by cube whisking as you go until your sauce is emulsified and glossy. Add a glug of dark rum, mix and then add the juice of 1 lime. Grate in a generous pinch of nutmeg. Leave to one side as you prepare the bananas.
Melt the remaining butter in a heavy based frying pan. Once the butter is melted add the bananas cut side down. Cook over a medium heat with the frothing butter until the base of the bananas have gone dark golden and slightly crisp on the edges.
Flambé the pan with a glug of rum and allow to cook for about 30 seconds. Turn the bananas over and pour in the butterscotch sauce.
Finish the bananas with a swirl of cream and turn off the heat.
Pour into a serving bowl or platter and grate over the zest of ½ a lime.
Serve immediately whilst the butterscotch sauce is still warm.