Kara Elder on vox.com:
The point of these open-faced sandwiches is to provide a quick, easy, somewhat nutritious lunch-time meal that provides sustenance without leaving you too full. They typically consist of two or three slices of bread, smeared lightly with butter, each topped with a single slice of cheese or meat, or perhaps a thin layer of jam, liver paste, or tubed caviar.
I never thought much of these while in Oslo — specially since Opera had a great lunch menu. But I’ve come to appreciate the simplicity of it years later.