Heat the oven to 200C/180C fan/gas 6. Line a muffin tin with cases. Mix 100g muesli with the light brown sugar, flour and baking powder in a bowl. Combine the milk, apple, oil and 2 tbsp nut butter in a jug, then stir into the dry mixture. Divide equally between the cases. Mix the remaining muesli with the demerara sugar, remaining nut butter and the pecans, and spoon over the muffins.
Bake for 25-30 mins or until the muffins are risen and golden. Will keep for two to three days in an airtight container or freeze for one month. Refresh in the oven before serving.