The Julebord "Christmas table" season starts in November. Rorbua in Aker Brygge
http://www.rorbua.as/ do quite a nice traditional "Juletallerken" (Christmas plate) with pork rib, sausages and meat patties in relaxed almost pub like surroundings. You could also try whale here too.
There are several other very good restaurants Aker Brygge too.