Cut the root end from the leeks and slice them in half vertically, then rinse throughly to remove all grit. Slice the leeks ands saute the olive oil over medium heat in a 2 quart saucepan. When the leeks are golden and soft add the garlic and cook for a minute, then add the amaranth, stock, bay leaf, and tomato puree, and bring to a boil. Reduce the heat to a simmer, cover and cook for 30 minutes.
Put half of the beans into a food processor bowl. Puree until smooth. When the amaranth mixture is done, remove the ba leaf, then carefully pour the mixture into the processor and puree. Cover the top of the feed tube with a folded towel as you process, to keep hot liquid from flying out. Pour the puree back into the pan.
Sire the remaining beans and the chopped herbs into the hot soup, and warm gently on the stove for 5 minutes or so. If desired, thin with water or more stock. Season with the salt and pepper to taste. Serve hot with whole grain bread.