Peel the apples and cut out the casing. Heat the butter in a pan and rub one of the apples with a little cinnamon and brown sugar until the sugar starts to caramelize. Put the baked apple and the raw apple with the oat flakes and yoghurt in the blender and blend until creamy on the highest setting. At the end, season with a touch of ginger and, if necessary, a little cinnamon.
If you want the smoothie to be more liquid, add some apple juice or milk.