Over the harsh Scandinavian winters, local cooks learned to make the most out of every animal they hunted. Nothing was wasted. They boiled hooves into gelatin, fried hearts into nuggets, and baked blood into pancakes.
Blood pancakes likely originated in Finland, where they are known as veriohukainen, but Swedes (who call the dish blodplättar) and Norwegians are also fans. While most recipes use pig or cow blood, any sanguine supply will do. The Sami people of northern Norway use reindeer.
In pancakes, blood operates as a handy egg substitute, chipping in protein and binding the milk and flour together. Unlike egg-based pancakes, however, these flapjacks turn dense, savory, and dark. They’re also packed with iron—which leads to a heartier breakfast while adding a copper flavor.
To counteract any metallic notes, cooks often throw in spices or sweeteners like molasses and top their finished creations with a sprinkling of sweet lingonberries or lingonberry jam. Some Sami chefs also cover the cakes with a sauce derived from cream, butter, and reindeer fat. The result is a rich, fatty breakfast that should fortify anyone to face another chilly day.
Source : https://www.atlasobscura.com/foods/blood-pancakes