Preheat the oven to 180C/350F/Gas 4. Line a 12-cup muffin pan with muffin cases, and set aside.

Using a food processor, pulse the Oreos into fine crumbs. Add the melted butter, and mix until all the crumbs are moist.

Press the mixture into the prepared muffin cases. Bake for 8 minutes, then allow to cool whilst preparing the cheesecake.

Using a handheld or stand mixer fitted with the paddle attachment, beat the cream cheese and sugar until combined.

Beat in the eggs, one at a time, then mix in the cocoa powder, zest and orange juice.

Divide the mixture between the prepared muffin cases, and bake for 20 - 22 minutes, or until the cheesecakes are just set.

Allow to cool completely in the pan on a wire rack, then refrigerate for at least 4 hours, or overnight.

For the ganache, place the chocolate and cream into a large microwave-safe bowl, and heat in 30 second intervals, stirring after each one, until melted and smooth.

Whisk in the orange juice and allow to cool for 5 minutes.

Pour the ganache over the tops of the cheesecakes, and chill until set.