Bill Holm's "Bread Soup" an old Icelandic Recipe. Enjoy.
Interestingly there is reference in this to cooking using a hot water spring for the heat. I actually did this back in 1968 in Iceland. Sadly it wasn't black bread soup but what an experience!

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Bill Holm was born in 1943 on a farm outside Minneota, Minnesota. He received a BA from Gustavus Adolphus College in 1965 and an MA from the University of Kansas in 1967. Holm was the author of several poetry collections, including Playing the Black Piano and The Dead Get By with Everything. His collection The Chain Letter of the Soul: New and Selected Poems was published posthumously in 2009. He also wrote several essay collections, including The Windows of Brimnes: An American in Iceland. A professor emeritus at Southwest Minnesota State until his retirement in 2008, Holm was known for his connection to Minnesota. In an article for the Minn Post, Nick Hayes describes him as “the quintessential voice of our small towns and prairies.” He goes on to note that Holm “was also our lost Icelander in Minnesota.” The grandchild of Icelandic immigrants, Holm spent most of his summers at his cottage in Hofsos, Iceland, and his writing was influenced both by the heritage and landscape of both of his homes. In 2008, Holm received the McKnight Distinguished Artist Award. He died on February 26, 2009, in South Dakota.