Very nice piece. I can see it being designed by Rolf Sinnemark, Bengt Edenfalk, or even Anna Ehrner at Kosta in the 70's or 80's but it doesn't show in any book or catalogue I have. Neither does the signature conform to how Kosta pieces were supposed to be signed (four digits before early 70's; five after). Although I've seen exceptions, but none like this, though. I've bought another Kosta catalogue which should be here soon. I'll check that when it arrives.
It's certainly worth trying to find out about.