Line the sides of a 20cm round loose-bottomed cake tin with greaseproof paper. Stir the butter into two-thirds of the biscuit crumbs and reserve the rest. Sprinkle the buttery biscuit crumbs over the base of the tin and press down. Soak the gelatine in cold water for 5-10 minutes until softened.
Heat the orange juice in a small saucepan until almost boiling. Squeeze any excess water out of the gelatine and then stir into the orange juice until dissolved.
Beat the quark, ricotta, vanilla and icing sugar together using an electric whisk until really smooth. Then, while the beats are still running, pour in the juice and beat until well combined. Pour the cheesecake mixture over the crumb base and smooth. Cover with cling film and place in the fridge to chill overnight.
To make the topping, tip the pitted cherries into a pan with the orange zest and 100ml water. Cook, with the lid on for fifteen minutes and then put one-third of the cherries into a bowl and mash with a potato masher to form a chunky compote. Return to the pan, add the jam, cornflour and 2 tbsp of water, mix to combine. Cook until thickened, if the sauce becomes too dry, add a little water. Leave to cool to room temperature.
Just before serving, remove the cheesecake from the tin and remove the greaseproof paper. Scatter over the remaining biscuit crumbs with some cherry sauce. Serve in slices with the remaining cherry sauce alongside.