Pre-heat the oven to 180°C / Gas Mark 4.
Butter and line a rectangular baking tin (approx 27cm x 20cm) with baking paper.
Thinly slice the apples and set to one side.
Place the butter and WHITWORTHS CASTER SUGAR and WHITWORTHS DARK SOFT BROWN SUGAR into a large mixing bowl and beat until smooth for 2-3 minutes add the eggs and vanilla and continue to beat for 2 minutes. Finally add the flour, baking powder and cinnamon and beat briefly to combine.
Spread half the mixture into the prepared tin. Arrange half the apples over the top of the mixture, and then repeat the process. Sprinkle over the WHITWORTHS DEMERARA SUGAR.
Bake for 45-50 minutes until golden and springy to the touch. Leave to cool for 10 minutes, then turn out of tin and remove paper. Cut into bars or squares.