I used to be a member of a family from Norway and Sweden. They served many dishes I have fond memories of, and know how to make.
But there is one I have been searching for and cannot find. It's called tjukkmjølk or tettemelk.
This sounds interesting - apparently you can dry it out and save this to make a new batch.
You might try one of these:
Sandi, I just ran across this question and I was curious so I did a little digging. I found these interesting links that have a lot of information. No recipe but more about the ingredients and process.
It sure sounds like you need to have the culture that was made with the butterwort to make it from scratch. And I can't find anyone who sells it commercially in the U.S. But I did find a comment that said that Långfil is the Swedish equivalent. And then I ran into this informative page.
Which led me to this Amazon link for the culture:
I can't tell if this will be exactly the same as what you had before but it is probably worth a try.
And last but not least, I found this page that appears to have a recipe for it. Unfortunately it is in Norwegian but maybe it will help.
Good luck and keep us posted. :)
Maybe a member of a Sons (and Daughters) of Norway Lodge could share a family recipe. Here is their webpage with a directory. members.sofn.com/