Preheat oven to gas 6 / 200C / 400F
Sift the flour into a bowl and add the xanthan gum if using, baking powder, soda, salt and sugar
Make a well in the middle and add the milk, butter, lemon juice, vanilla and mashed banana
Mix into a batter, then fold in blueberries. You may need to add a few extra tablespoons milk if using gluten-free flour. Let the mixture stand for 5 minutes and check the consistency. It should be quite a thick batter
Spoon into 12 paper cases and bake for 15 - 20 mins. You can sprinkle some golden caster sugar or brush with a little milk then put back to bake after 15 minutes for another 5 minutes. This is just to help with colouring due to there being no egg in the recipe, it doesn't matter if you do that step or not
Take out of the oven and let cool in the tin covered in a clean dishtowel for 30 minutes before removing the paper cases
You can sub the banana for a quarter of a cup / 60mls of another puree such as apple, pear, raspberry or cherry which make the cakes a pretty pink colour or a vegetable puree such as courgette or avocado which is my own personal preference as it imparts no flavour
