Preheat oven to 190°C and grease a 23cm spring-form tin with butter and flour.
Melt 25g butter in a pan with Bramley apples, water, and caster sugar.
Cover and cook for 4 minutes until thick, then beat in calvados until smooth.
Cream 90g butter and light brown sugar in a bowl until light.
Mix in golden syrup, eggs, and vanilla extract.
Fold in the self-raising flour.
Stir bicarbonate of soda into the apple puree and quickly combine with the batter.
Pour into the tin and bake for 30 minutes.
Arrange sliced apples on top, brush with 25g melted butter, sprinkle with sugar, and bake for 15 more minutes.
Melt sauce butter and dark brown sugar together, then stir in cream and calvados.
Simmer sauce for 5 minutes until thickened and serve over cake slices with ice cream.