Ellefsen is a nice place where you wouldn't so much expect a restaurant to be (in front of a gas station, and where it's more residential than commercial).
The food is fresh, service is delightful, and their menus are always amazingly original. The smørgås and gravlax are my big favourites. They also have very nicely presented desserts. And a very charming selection of wines.
Lovely for a chat with a friend, or reading a good book. The Wi-Fi is not always liable, though.