I have seen this lots of times in flighht during night.
When the indoor cabin lighting is dimmed strongly it is rather easy to see stars through the aircraft windows.
The newer the aircraft, the better (although I did not fly on a 787 or 350 yet) due to larger windows, better glass (or composie material ?) quality and LED mood lighting appears less intrusive than fluorescent or halogen cabin lighting on older aircraft.
I even took photos by wrapping the camera in a blanket and putting the window shutter down to the upper side of the lens to prevent any reflections, pushing it towards the window, breathing out (which makes my hand more steady) and expose a few seconds.
Obviously, there should be no turbulence.
Here some results:
http://skysurfer.eu/extremeastro.php
Mostly the sky is clear (above the clouds), unless one is flying in the tropics where cirrus clouds can reach to 15km (50000 ft, well above aircraft ceiling of 43000ft).
The sky appears darker when there is moonlight as there is less air above, stars very close to the horizon are easily visible.
What are your experiences ?