Preheat oven to 180 C / 356 F / gas mark 4.
Place paper baking cases in a muffin tin.
Mash the bananas until smooth
Mix in the sugar, vegetable oil and vanilla.
Add the dry ingredients and stir just until combined: remember not to over mix.
Spoon the mix into the baking cases then transfer to the oven to cook for 18 - 20 minutes.
Remove from the oven when they are golden brown and a skewer inserted in the middle comes out clean.
Once cooked remove from the baking tray and leave to cool.
In the meantime melt the vegan butter and add caster sugar to a bowl.
Brush the melted sugar over the muffin tops and dip in the caster sugar. Shake off any excess.
Enjoy while still warm.