Line a 1 kg (2 lb) loaf tin with nonstick baking paper. Sift the flours and baking powder into a large bowl. Mix in the sugar, peanut butter, butter, eggs, vanilla extract and apple juice. Stir through the chocolate chips and apple.
Spoon the mixture into the prepared tin and bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 1 hour. To see if it is cooked, insert a skewer in the centre of the loaf – if it comes out clean it is done, but if cake mix is attached to the skewer it will need another 10 minutes.
Remove the cake from the oven and turn out on to a wire rack. Peel off the baking paper and leave to cool. Serve cut into slices.