Do you mean Boston Brown Bread?
Is a traditional American bread made from mixed grains, usually a blend of rye and wheat flour with cornmeal, buttermilk and molasses. Raises with bicarbonate of soda, the mixture is placed in a tall cylindrical mold and steamed, not dry baked in the normal way. The Puritan community of New England served this bread on the sabbath with Boston baked beans.
Source: Davidson, Alan. 1999. The Oxford Companion To Food. Oxford: Oxford University Press