I’m pretty sure I’ve posted this number by Sissel here before (though not this performance, which conveniently includes subtitles). But it’s high on my list of Norwegian Christmas songs that deserve to be known outside the neighborhood.
According to this Norwegian account, the lyrics come from a poem by Jakob Sande. It was first published in 1931, but the author didn’t think much of it. When Lars Soraas, who was putting a Christmas songbook together in 1948, asked him for permission to use it, Sande had forgotten about it completely. Since then it’s become his best-known work.