Hi Morten, the other way you can try to surface something that has an irregular boundary like that is to extend some pieces of the boundary so that they make one longer curved side and then surface that and then cut off some of that surface to make the final end shape, rather than trying to directly construct a surface along all those curves.

So in your case here that could mean something like put in a blend curve between these 2 curves here:



That then basically continues a smooth curve for those top pieces like this:



Repeat that on the other side, join those pieces together and do a Rebuild on them, and then you have a 4 sided boundary like this which can then be surfaced with Sweep or Network:



Then you slice off the ends with a line to get your final shape: