I have several pieces of this pottery, but know very little about it. The bottom is usually marked with Elle, Norway, and some codes and/or a signature. The word "EllE" is often written in a stylized script that looks like two Es with two small dots or slashes between them. Some pieces also have a sticker label saying Elle, Norsk.
There seems to be very little information on these pottery companies online, at least in English. Some online sources say that the Elle studio was started in 1942 in Torkildstranda in Drøbak near Oslo, that it was led by Tor Samuelsen, and that it produced pottery up until 1967.