I made another orange cake and decided to try a Thermomix frosting for it so...
I took the peel of one orange, and 500g icing sugar and blitzed it for 8 seconds at speed 9. Give it longer of you want a really smooth frosting for piping, I didn't, I want to see little specks of real orange zinginess.
Add 100g unsalted butter, mix 20 sec speed 7
Add 25ml milk, 10 ml vanilla, mix 10 sec speed 7
Insert butterfly and mix 3 mins at speed 3
Refridgerate 10-15 mins before using ( I put mine in the fridge in the TM bowl and whizzed it again for 5 secs after thickening)