Preheat oven to 180ºC while you make base. Line the base of a springform tin, that will fit inside your Varoma dish, with baking paper.
Place biscuits and butter into Thermo bowl and blend 30 sec/speed 6 until clumping together when pushed. (I found amazing jaffa wafers at Ikea, orange biscuit, with a choc chip…but like I said, plain will do.)
Press into tin and bake 10 minutes. Remove and cool.
Without cleaning, place zest and sugar into Thermo bowl and mill 10 sec/speed 10.
Add remaining ingredients except chocolate and blend 30 sec/speed 8. Scrape down sides of bowl and repeat. Remove from bowl and set aside.
Rinse bowl and place enough water to reach 3/4 full mark. Bring to the boil, 8 min/Varoma/speed 3.
Set Varoma dish into position. Place cooked base into Varoma and pour the prepared filling into the springform tin. (It is easier to do it this way, less spillage!)
Place pieces of the chocolate into the filling, they will disappear, but try and get a few to remain on the top.
Steam 60 min/Varoma/speed 3. Check water level and add water as needed.
Steam 40 min/Varoma/speed 3. Do not mop up any liquid that may be on top of the cheesecake. Allow to cool slightly before refrigerating for several hours.
Serve garnished with Persian fairy floss (pictured) and do not put this onto the cheesecake if using, literally as you are serving it in slices as it will melt and become very, very unattractive in a hurry. Another option for garnish would be grated chocolate, or chocolate curls, commercial orange jelly slices, or glazed orange slices.