Preheat the oven to 180°C, fan 160°C, gas 4. Lightly butter a 23cm round, spring form tin and line the base with a circle of baking parchment.
Place the biscuits in a food processor and whizz to crumbs. Pour in the melted butter and demerara sugar and pulse a couple of times to mix. Tip the crumbs into the base of the tin and press down to make the surface level. Chill in the fridge while you make the topping.
Using a wooden spoon, mix together the cream cheese, caster sugar, flour and vanilla seeds, in a large bowl, until combined. Gradually add the eggs, stirring until incorporated, then pour the mixture over the chilled base.
Place the cheesecake on a baking tray and bake for 45-50 minutes, until the filling has just set. Cover with baking parchment if the top is browning too much.
Remove from the oven and leave to cool for 10 minutes. Slide a palette knife around the outside of the cheesecake to ease it from the tin, then leave in the tin to cool completely.
Once cool, remove from the tin and transfer to a serving dish. Spread with the soured cream, top with the berries and serve in slices.