QF often do ice creams on a stick in short haul. They have exactly the same issue - the thing usually comes out solid as a rock.

Also, last week I was on a QR flight in J and ordered an ice cream sundae-type desert, after a bit of stalling the FA came over to me, apologized, and said the ice cream was still far too hard for them to be able to even make it.

Seems like serving ice cream on a plane is just hard to do.