Make the topping first by placing all the topping ingredients into the food processor bowl and process with the metal chopping blade until the butter is chopped into small pieces. Do not over process or the rolled oats will be chopped too fine.
Tip topping out of the bowl.
Without washing the bowl add in the apples which have been cored and cut into about 12 pieces. There is no need to peel them first.
Process with metal blade until cut into fine pieces.
Add the remaining cake ingredients. It is not necessary to sift the dry ingredients first but make sure the baking soda is not lumpy.
Line the base of a 9"/23cm tin with baking paper & butter or spray the sides.
Pour batter into prepared tin.
Sprinkle over the topping mix.
Bake at 350'F/180'C for approx 40-45 minutes or until the sides of cake shrink from the edge of the tin and the centre springs back when pressed lightly.
Serve hot, warm, reheated or cold with whipped cream and/or custard as a dessert or cold in lunchbox.