Heat the oven to 190C/375F/Gas 5. Melt the lactose free butter and allow to cool. Mash the bananas well. Sift the gluten free flour, baking powder, bicarbonate of soda, salt, cinnamon and nutmeg together in a large bowl, add caster sugar and stir through.
With a fork, beat together the eggs, vanilla extract, melted lactose free butter and milk in a second bowl. Add the mashed banana and stir through.
Make a well in the centre of the dry ingredients and add the egg mixture, stirring roughly with a fork (don't over mix) until it is a lumpy paste.
Set paper cases into the moulds, or grease the moulds well with a little extra oil or lactose free butter and spoon in the mixture until almost full.
Bake for 20 to 25 minutes or until the muffins come away from the side of the pan when touched. Rest the muffin tray on a wire rack for five minutes then remove the muffins and leave on the rack for another five minutes before serving.