Preheat an oven to 180°C/ 160°C fan/ gas mark 4.
Line a 20cm round cake tin with baking paper.
Into a large mixing bowl, stir together the Bread Mix, egg replacer, baking powder, spices and brown sugar.
Rub the butter into the mixture with your fingertips until the mixture resembles breadcrumbs.
Peel the apple, cut into quarters and discard the core. Thinly slice one quarter of the apple and reserve for decoration. Dice the rest and stir into the mixture along with the ProZero until fully combined.
Spoon the batter into the cake tin and level with a spatula. Use the remaining apple slices to decorate the top, before sprinkling over the demerara sugar.
Bake for 55-60 minutes, until a skewer inserted into the centre of the cake comes out clean. Allow to cool before removing the tin.