Cut the pandoro - cut it in half vertically, and continue cutting into half inch thick pieces. The pieces will be very large at this point. Cut them down smaller so that they fit in the pan and cover the surface of the pan.
In the bowl of a stand mixer, whip cream, sugar and vanilla extract together. Whip until thick but not yet holding peaks. Add mascarpone to the mixture, and continue whipping until the mascarpone is fully mixed in, and the cream is velvety and smooth in texture, and holding stiff peaks.
Pour cold coffee in shallow dish. Mix in the amaretto or rum. Dip half the pandoro pieces into the coffee, ensuring that they are covered in coffee, but not soaking wet (this will make the tiramisu too soggy). Add the pandoro pieces to the pan in a single layer.
Top with half the mascarpone mixture and level out. Dust with cocoa powder.
Dip the remaining pandoro pieces in the cold coffee and add this second layer of pandoro pieces to the pan. Top with remaining mascarpone/cream mixture.
Cover with saran wrap and refrigerate for at least 2 hours. Dust with cocoa powder before serving.