Preheat oven to a moderately hot 200°C/ 180°C (fan-forced).
Line a 12-hole standard muffin pan with baking paper-cases.
Sift flour and bicarbonate of soda into a bowl. Add the sugar, salt, cinnamon and mixed spice. Stir through the flour. Make a well in the centre.
In a jug mix together the milk, eggs, butter, mashed bananas and vanilla extract. Pour this mixture into the dry ingredients.
Fold the mixture gently with a metal spoon until just combined. Be careful not to overbeat the mixture or the muffins will become tough and rubbery. The mixture should still be lumpy.
Divide equally among the paper cases, filling each hole to about three-quarters full. Sprinkle with rolled oats and extra caster sugar. Bake muffins for approximately 20-25 minutes until golden and cooked through.
Notes
Leave the muffins in the pan for 5 minutes, then turn onto a wire rack to cool. Eat warm or chilled with icing. Cold muffins can be frozen for up to 3 months in a freezer bag.Flour - Self-raising flour can be substituted with other flours. If using plain flour or spelt flour, add 2 teaspoons baking powder along with the bicarbonate of soda.