Makes 2 loaves
Sprinkle dry yeast and sugar over 1/2 cup warm water (105 - 115 F) in small bowl and stir to dissolve. If using cake yeast, crumble into small bowl. Stir in sugar and 1/2 cup lukewarm water (95 F). Let mixture stand until foamy, about 10 minutes.
Meanwhile, heat 1 cup water, buttermilk, butter and honey in heavy small saucepan to lukewarm (95 F), stirring until butter melts. Combine graham flour, granola, oats, walnuts and salt in large bowl. Add yeast and lukewarm liquid mixture, then egg, whisking until thick, about 5 minutes. Using wooden spoon, mix in enough all-purpose flour 1/2 cup at a time to form soft dough. Knead on floured surface until smooth and elastic, kneading in more all-purpose flour if dough is sticky.
Grease large bowl and add dough, turning to coat entire surface. Cover bowl with plastic. Let rise in warm draft-free area until dough is doubled in volume, about 1 hour.
Grease two 9x5-inch loaf pans (preferably black steel). Gently knead dough on lightly floured surface until deflated. Cut dough in half. Pat each piece out into rectangle. Roll up jelly roll fashion, pinching seams to seal. Place seam side down in prepared pans. Cover with towel. Let rise in warm draft-free area until doubled in volume, about 45 minutes.
Preheat oven to 375 F. Bake until loaves sound hollow when tapped on bottom, about 40 minutes. Immediately remove from pans. Cool completely on wire racks.