This is another Ruby Tandoh recipe which you can find here – I made a few adjustments, firstly because I did not have amaretti biscuits, so I added a drop of almond extract to the base; secondly, before adding the coffee, I could not resists saving a bit of the filling, to which I added 1 tsp of sherry, then poured it over the coffee filling and swirling around a knife I created a marbled effect… such fun!
for the base:
75g unsalted butter
100g digestive biscuits
50g amaretti biscuits
for the filling:
3 tbsp instant coffee granules
3 tbsp hot water
500g mascarpone
125g light brown soft sugar
3 tbsp cornflour
2 tsp vanilla extract
A pinch of salt
3 large eggs
1 tbsp cocoa powder, for dusting
Preheat the oven to 180C/350F. Melt the butter over a low heat while you crush the biscuits to a fine rubble in a large bowl. Stir the butter into the biscuits until the powder holds together in clumps when squeezed. Press the mixture into a 20cm round spring-form cake tin, packing it firmly under the back of a spoon. It’s important to properly compact the mixture otherwise rogue crumbs will float upwards through the cheesecake mixture during cooking, pockmarking the dessert’s surface.
Bake the base for 10 minutes, keeping a close eye on it, to make sure that the biscuits don’t burn. It should be just about firm.
Leave the base to cool slightly while you prepare the filling mixture, and turn the oven down to 140C/275F. This might seem like too low a temperature to bake with, but it’s this long, slow cook that’ll give the cheesecake a perfectly smooth texture. You can achieve a similar result by baking the cheesecake in a water bath, but I’ve had too many disasters with flooded cheesecakes to sincerely be able to recommend that method.
Dissolve the coffee granules in the hot water then set aside to cool slightly. 
Stir the mascarpone with the sugar and cornflour in a large bowl until smooth and lump-free. Add the vanilla extract and salt. Add the eggs one at a time, stirring well between each addition. Finally, mix in the cooled coffee.
Pour the cheesecake mixture over pre-baked base and bake for 1–1¼ hours: be patient with it, give the cheesecake as long as it takes for it to just about set. When lightly jiggled, it should barely shimmy at its centre and be firm at the edges. 
If you overcook it, waiting for it to be perfectly solid all over, it’ll be more likely to crack as it cools.
Leave the baked cheesecake to cool in its tin before gently unmoulding and chilling. Just prior to serving, lightly dust a little cocoa powder over the top.
yummmmmmm 🙂