Add all ingredients for the dough to your bread machine and make the dough as per manufacturer's instructions.
When the dough is ready, pre-heat the oven to 175ºC (350ºF) and grease a small-medium skillet.
Heat the butter and set to one side. Take the dough from the machine (it is very sticky) and quickly knead for around 30 seconds on a well-floured surface. Using a rolling pin, roll out the dough into a large rectangle (around 40x50cm) with one of the shorter sides facing you (you will need to work the dough hard as it will be so elastic it will fight you every step of the way - that's a good sign).
Mix the sugar, vanilla sugar and 1 tablespoon of cinnamon together in a bowl and add the melted butter. Mix to combine. Dollop little bits of the filling all over the dough and spread it about with a knife (there will not be enough to fill every inch of the dough but you don't need it to). If you love cinnamon, sprinkle a further 1 tablespoon over the gaps not covered by the filling.
Taking a pizza slicer, cut the dough into around 8 strips of about 4-5cm thickness. Starting with the first strip, roll it all the way up to the top. Move it over to the start of the second strip and repeat. Continue to do so until you've used up all the strips of dough. It's not an easy process at all especially when your bun roll gets bigger, but it doesn't have to be perfect - mine most certainly wasn't. If you are unsure what I mean with these instructions, take a peek at the video link above.
Place on the skillet, cover and let rest for around 20-30 minutes. Then bake in the oven for around 18-20 minutes. Make sure it is baked but don't over-bake it. Remove from the oven and allow to cool.
For the drizzle: add two tablespoons of milk to a bowl and gradually add just enough icing sugar to make a thick paste. Pour it over the giant bun, slice and enjoy.