In large bowl, combine 3 cups flour, sugar, undissolved yeast,
salt, and baking soda. Heat buttermilk, water, and butter until
very warm (120 to 130oF); butter does not need to melt.
(Mixture will appear curdled.) Stir into dry ingredients. Stir in
enough remaining flour to make soft dough. Knead on lightly
floured surface until smooth and elastic, about 6 to 8 minutes.
Cover; let rest on floured surface 10 minutes.
Divide dough in half. Roll each half to 12 x 7-inch rectangle.
Beginning at short end of each, roll up tightly as for jelly roll.
Pinch seams and ends to seal. Place, seam sides down, in 2 greased
8 1/2 x 4 1/2-inch loaf pans. Cover; let rise in warm, draft-free
place until doubled in size, about 30 to 45 minutes.