In a large bowl, combine the first six ingredients. In another bowl, whisk the buttermilk, molasses, brown sugar and oil. Stir into dry ingredients just until moistened. Fold in walnuts and raisins. Transfer to a greased 8x4-in. loaf pan; cover with foil.
Place pan on a rack in a boiling-water canner or other large, deep pot; add 1 in. of hot water to pot. Bring to a gentle boil; cover and steam for 45-50 minutes or until a toothpick inserted in the center comes out clean, adding more water to the pot as needed.
Remove pan from the pot; let stand for 10 minutes before removing bread from pan to a wire rack. Serve with cream cheese if desired.