In a large mixing bow., dissolve yeast in warm water. Add sweet potatoes, 1/2 C. butter, honey, egg, salt and whole wheat flour. Beat until smooth. Stir in enough all purpose flour to form a soft dough. Turn into a floured surface; knead until smooth and elastic, about 6 - 8 minutes. Place in a greased bowl, turning once to grease the top. Cover and let rise in a warm place until doubled, about 1 hour.
Punch down dough. Turn onto a lightly floured surface; divide in half, shape into 2 loves. Place into 2 greased 9" X 5" X 3" loaf pans. Cover; let rise until doubled, about 25 minutes. Bake at 375° for 40 -45 minutes or until golden brown. Cover loosely with foil if to browns t quickly. Remove from pans to wire racks. Melt remaining butter and brush over warm bread. Cool. Spread in a small bowl, beat butter and cream cheese until fluffy. Stir in walnuts. Serve with bread.
