Preheat the oven to 180 C / Gas 4. Grease the bottom of a 20cm loose bottomed cake tin and line with parchment.
Stew the apples, water and 55g sugar in a pan over medium heat until soft, about 10 minutes. Stir in the cinnamon and sultanas; allow to cool.
Place the flour and semolina in a bowl and rub in the butter with your fingertips until it resembles coarse breadcrumbs; stir in the 55g caster sugar. Spread half of the crumble mixture into the bottom of the prepared tin.
Bake in the preheated oven until firm, about 10 minutes. Spread base with the apple mixture and top with remaining crumble. Return to the oven and bake until the top is crisp and golden, 15 to 20 minutes.