Preheat the oven to 180°C (fan oven 160°C), gas mark 4. Line the base and sides of a deep, 20 cm (8 inch), loose-based, springform cake tin with greaseproof paper.
Put the conserve in a small saucepan with 50 ml (2 fl oz) of the orange juice and stir over a low heat. Bring to the boil and bubble gently for 5 minutes until reduced by about half. Add in the blackberries and leave to cool.
Rub 25 g (1 oz) of the butter and 25 g (1 oz) of the caster sugar into the flour. Stir in the granola cereal and spread out on a foil-lined baking sheet. Bake in the preheated oven for 10-12 minutes until golden brown. Leave to cool, then break into rough crumbs with a fork.
Reduce the oven temperature to 170°C (fan oven 150°C), gas mark 3.
Melt the remaining butter in a small saucepan and stir in the crushed biscuits. Press the crumbs over the base of the lined tin and set aside.
Beat together the cheeses, eggs, orange zest and remaining sugar with the soured cream until smooth. Spoon onto the biscuit base and bake for 1.25 hours in the oven.
Open the oven door and pull the cheesecake out a little. Drizzle the blackberries and their liquid randomly over the surface and return to the oven for a further 1 - 1.25 hours until the cheesecake feels just firm when touched in the centre.
Sprinkle over the crumble mixture, leave to cool and dust with icing sugar before serving.
The cheesecake can be made ahead and kept in the fridge for up to 3 days without the crumble topping. It also freezes well.
Mixing goat's cheese with the soft cheese gives a slight acidity to the filling which offsets the richness. However, it can be omitted - just use 600g (1lb 6oz) full-fat soft cheese.
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