Note Rapadura sugar is available from select health-food shops and delicatessens. If unavailable, substitute dark brown sugar.
The buckle is a dense fruit-studded cake with a crumbly crunchy top. We've added rapadura sugar for its more-ish, complex caramel-molasses flavour. You can sweeten the crème fraîche with a little rapadura sugar too - it's a heavenly combination. This cake is best eaten on the day of making.