1. Preheat oven at 170-190 degree C or 350 degree F.
2. In a large mixing bowl, sift self rising flour.
3. Add caster sugar, and brown sugar to it. Mix well.
4. Make a well in the centre of the bowl, and add milk, egg, butter, and vanilla in it. Mix gently to incorporate. Do not over mix.
5. Drop blueberries in it. Fold to spread evenly.
6. Grease a muffin tray with cooking spray, and spoon mixture in it.
7. Pop it in oven, and bake for 20 minutes or until golden and firm to touch.
8. Remove from oven, and allow it to cool for 10 minutes on wire rack.
9. Serve blueberry muffin with a cup of hot tea.