Preheat the oven to 325°F. Mix crushed digestive biscuits with melted butter and press into the bottom of a springform pan to form the crust.

In a microwave-safe bowl, melt the chocolate chips with 0.75 cup of heavy cream, stirring until smooth. Set aside to cool.

In a large bowl, beat the cream cheese and sugar until smooth. Add eggs one at a time, then vanilla and cocoa powder, mixing well.

Fold in the melted chocolate mixture. Pour the filling over the prepared crust. Bake for 105 minutes or until set.

Allow to cool completely, then refrigerate for at least 4 hours before serving. Top with chocolate ganache.