Brunost - literally brown cheese - is the dense, sweet, caramelised whey cheese that ranks as one of Norway's most distinctive food products. The standard variety, gudbrandsdalsost, is made from a blend of cow's and goat's milk with cream, slow-cooked for many hours until the whey caramelises into the characteristic brown color and intense malty-sweet flavour. The cheese was invented in the Gudbrandsdal valley in 1863 by the dairymaid Anne Hov, whose innovation was to add cream to the previously thin whey-cheese tradition; the result became a Norwegian national staple within a generation.
The flavour is unlike anything in the wider European cheese tradition. It is sweet, not in the way that a young goat cheese is mildly sweet but in the way that dulce de leche or condensed milk caramel is sweet - with a long, almost coffee-like finish from the slow caramelisation of the milk sugars. The texture is dense and slightly fudge-like rather than crumbly. The cheese keeps unusually well, which made it valuable historically as a mountain and travel ration; a small block in a backpack on a multi-day mountain trip remains a very Norwegian thing to carry.
The classic Norwegian preparation is to slice it thinly with a special wide-bladed cheese plane (ostehøvel, also a Norwegian invention, dating to 1925) and serve it on dark rye bread or warm waffles. The pairing with multer on bread is the Norwegian classic. The pairing with hot waffles, sour cream and jam is the søndagsfrokost - Sunday breakfast - equivalent of what a French would call viennoiserie.
Brunost has had a long second life internationally as a curiosity. It was featured in the New York Times food section in 2014 in a piece titled The strangest cheese you will love, and has appeared in successive Bon Appétit, Saveur and Eater features. It remains an acquired taste for many international visitors but is a staple at every serious Norwegian breakfast spread. It travels well as a souvenir - vacuum-sealed blocks are widely available at the Bergen fish market, the Mathallen food hall in Oslo, and most airport duty-free shops.