Begin by crushing the digestive biscuits in a food processor until fine crumbs form. In a bowl, mix the crumbs with unsweetened cocoa powder, caster sugar, and melted unsalted butter until well combined.

Press this mixture firmly into the bottom of a springform tin to create a solid base. Refrigerate the crust for 20 minutes to set while you move on to the next step.

Preheat your oven to 160°C (320°F) for fan-forced or 165°C (330°F) for conventional baking. Prepare a large roasting pan filled with boiling water.

In a large mixing bowl, beat the full-fat cream cheese until smooth. Gradually add in the caster sugar and mix well.

Incorporate the large eggs one at a time, followed by sour cream, vanilla extract, plain flour, and cooled espresso mixture until rich and glossy.

Pour the creamy filling onto the chilled biscuit base. Wrap the bottom of the tin in aluminum foil to prevent water from seeping in.

Carefully place the wrapped tin in the prepared roasting pan filled with hot water, and bake for 50-60 minutes until edges are set.

Once baked, turn off the oven and crack the door open. Let the cheesecake cool for about 30 minutes in the water bath.

Transfer the cheesecake to a wire rack to cool completely, then refrigerate overnight for optimal firmness.

To make ganache, heat heavy cream until simmering. Pour over chopped dark chocolate and espresso powder. Stir until smooth.

Allow ganache to cool slightly at room temperature, then spread evenly over the top of the cheesecake.

Chill the decorated cheesecake for about 30 minutes before slicing and serving.