Preheat the oven to 150°C and line a 30x30cm cake tin with parchment.
Boil apples in 300ml water for 2 minutes.
Add bicarbonate of soda and blend into a puree.
Cream butter and sugar then beat in the eggs.
Stir half of the apple puree into the mixture.
Fold in the flour and baking powder.
Bake in the tin for 45 to 60 minutes until golden.
Whisk custard ingredients over simmering water until thickened.
Melt toffee sauce ingredients in a pan and keep warm.
Increase oven temperature to 180°C.
Rub crumble ingredients together and bake on a tray until golden.
Whip cream with icing sugar and vanilla to soft peaks.
Plate with apple puree, cake, sauce, and custard.
Garnish with Chantilly cream, crumble, and dusted icing sugar.