125 ml (4 fl oz) rapeseed oil, plus extra for cooking
Mix together the sugar, apple, blackberries and cinnamon in a bowl.
Sift the flour and baking powder into a separate bowl and make a well in the centre. Mix together the eggs, milk and oil in a jug, then pour into the well and stir until blended. Stir in the fruit mixture, taking care not to over-mix. Divide the mixture among the sections of a lightly oiled or paper case-lined 12-hole muffin tin.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 20–30 minutes or until a skewer inserted into the centre comes out clean. Transfer the muffins to a wire rack to cool. The muffins can be stored in an airtight container for up to 3 days.