How to use a bottom concave ebelskiver (Æbleskiver) pan on a glass cook-top stove?
You could consider heating it up, while empty, in an oven (I would go for, say, 200C/390F). Keep it there for at least 30 minutes: the transfer of heat from the air to the cast iron is not very efficient! Then take it out quickly, pour the batter in, and return it to the oven until done (and then make the next batch, if you're making multiple).

An issue with this could be that the Æbleskiver might cook too quickly from the top. You might need to experiment with the target temperature you leave the oven at.