Preheat oven to 180 (gas 4). Pop some paper muffin cases into a muffin tin. Depending on how big you make your muffins this recipe can make between 9-12 muffins
In a large mixing bowl, sift together the gluten-free self-raising flour and baking powder. Whisking these dry ingredients together ensures even distribution and helps prevent lumps in your batter.
In a separate bowl mix the oil and sugar and combine well. This will help to make your muffins light and fluffy.
Beat in the eggs one at a time, mixing well after each addition. Don't worry if the mixture looks a bit curdled at this stage - it will come together when you add the dry ingredients.
Stir in the mashed bananas, sultanas and vanilla extract. The riper your bananas, the more flavour they'll impart to your muffins.
Gradually fold in the dry ingredients, alternating with the milk if needed. Start and end with the flour mixture, and be careful not to overmix. A few small lumps are fine - overmixing can lead to tough muffins.
Pour the mixture into the muffin cases.
Bake in the oven for 20 minutes until golden brown.
To check if it is cooked through pop a skewer inside if it comes out clean it is fully cooked (if it isn't fully cooked keep cooking and checking in 5-minute intervals until done).
Allow to cool for a few minutes then remove the muffin cases from the tin onto a wire rack to fully cool.
Serve with custard, maple syrup or on its own, delicious.