Start by preheating the oven to 200C (390F). Line a cast iron skillet with parchment paper (I find this makes clean up so much easier - and we are going for quick here remember).
In a medium size bowl, whisk together the all purpose flour, sugar, baking powder, baking soda and salt. Set this aside.
In another bowl, whisk together the buttermilk, sourdough starter, melted butter and egg. It should should be well combined and have minimal lumps.
Now, pour the liquid ingredients into the dry ingredients and bring together into a sticky dough using a spatula. The dough won't be like the sourdough you're used to, this is quite a sticky dough (it's sort of like biscuit dough).
Lightly flour a clean counter top and tip the dough out. Lightly dust some flour over the top and gently use a rolling pin to roll the dough out into a rectangle (we aren't looking for perfection here). The rectangle needs to be around 25cm x 35cm (10" x 14"). Try not to add too much flour here - a stickier dough leads to fluffier rolls.
Now, once the dough is rolled out, spread the softened butter from the filling ingredients all over the rectangle, leaving a small gap at the top.
Then mix the brown sugar and cinnamon together and sprinkle that all over the butter you just spread out.
Carefully roll the dough up into a log. You can use a metal dough scraper to help if the dough is a little sticky. Now, as you can see from the photos, these are not perfect cinnamon rolls, but we are going for quick and easy here! Plus the frosting will hide the tops anyway!
Once you've rolled up your log, cut the log into 1" pieces (around 2.5cm). I just used the blade of my knife to measure to make it easier. Arrange the no wait sourdough cinnamon rolls into the cast iron skillet you prepared earlier.
Bake for 20 minutes at 200C (390F) or until just starting to brown on top.
While the no wait sourdough cinnamon rolls are baking, add the cream cheese, butter, powdered sugar and vanilla extract to the bowl of a stand mixer and whip until light and fluffy. Set aside until the rolls are baked through.
Remove from the oven and allow to cool slightly before smothering in the vanilla cream cheese frosting.