Make the butterscotch first so it has time to cool to room temperature before you need it
Melt the mararine in a pan over a medium heat. First whisk in the brown sugar, then whisk in the thick coconut milk
Let bubble for 5 minutes without stirring
Take off the heat, whisk in the vanilla and salt then let cool to room temperature
Preheat the oven to gas 6 / 200C / 400F and line a 12 hole cupcake tin
Sift the flour into a bowl and add the xanthan gum if using, baking powder, bicarb of soda and sugar
Make a well in the middle and add the milk, lemon juice, melted margarine, vanilla and mashed banana
Stir into a smooth batter
Pour evenly between the cupcake liners
Bake for 15 - 20 minutes until risen and firm to the touch
Cover with a clean tea towel and let sit for 30 minutes to cool
Meanwhile, to make the buttercream, whisk the softened margarine with the powdered sugar until light and creamy. Beat in the milk and vanilla extract. Add more icing sugar if the buttercream is too thin or more milk if it's too thick to pipe
Fill a piping bag (thin nozzle) with some of the butterscotch sauce and push the tip into top of each cupcake once cooled, applying enough pressure to fill each with some sauce
Fill another piping bag (wide nozzle) with the buttercream and swirl on generously
Drizzle with the remaining butterscotch sauce - the more the better!
