Preheat the oven to 200°C, and line an 8inch, loose bottomed cake tin with baking parchment.
In a large bowl, mix together the quark, Philadelphia, eggs, granulated sweetener and chocolate extract. Add the coffee granules to the boiling water and add to the mixture. Sift in the cornflour and cocoa powder and stir well to ensure it is thoroughly mixed.
Pour the mixture into the lined cake tin and bake for 10 minutes in a hot oven. Turn the oven down after this time to 140°C and bake for a further 25 minutes. Check the mud pie after this – it should have a slight wobble with no runniness.
Leave to cool completely and refrigerate for an hour before adding the topping.
For the topping
In a dry frying pan, add the caster sugar and oats. It is important to use sugar and no sweetener for this. Leave on a moderate heat, moving the pan occasionally until the sugar has melted and oats have toasted. Leave to cool.
Once the ujd pie has been refrigerated, take the choc shot and spread gently around the edge of the top of the cheese cake. Crush up the caramelised toasted oats as you sprinkle them around the edge and pat gently so they stick to the choc shot.
Using a fine grater, grate over the dark chocolate into the centre of the cheesecake. Slice into 10 pieces and serve.