Ingredients
5 cups bread flour, divided2 cups plus 1 tablespoon rye flour, divided1/2 cup potato flour1/3 cup nonfat dry milk powder2 tablespoons sugar2 tablespoons caraway seeds3 teaspoons instant or quick-rise yeast2-1/2 teaspoons onion powder2 teaspoons salt2-3/4 cups warm water (110° to 115°)1/4 cup vegetable oil2 tablespoons dark baking cocoa1 large egg, lightly beaten with 1 tablespoon water
Preparation
In a large bowl, whisk together 4 cups bread flour, 2 cups rye flour, potato flour, milk powder, sugar, caraway seeds, yeast, onion powder and salt. In another bowl, whisk together warm water and oil; pour over flour mixture and stir until combined. Dough will be sticky. Turn dough onto a lightly floured surface; with floured hands, knead dough, incorporating remaining 1 cup bread flour as needed until dough becomes smooth and elastic, 8-10 minutes. Divide dough in half. Mix dark cocoa powder with remaining 1 tablespoon rye flour; knead cocoa mixture into 1 portion of dough until fully incorporated.
Lightly coat 2 large bowls with oil. Place 1 portion of dough into each bowl and turn to coat. Cover and allow dough to rise until doubled in size, 1 to 1-1/2 hours. Working with 1 portion of dough at a time, turn onto lightly floured surface; roll each into a 14x12-inch rectangle. Place dough with cocoa on top of remaining dough; starting with a long side, roll jelly-roll style to form a spiral, pinching seam together to seal. Place seam side down in a greased 13x4-inch Pullman loaf pan, tucking ends under to form smooth loaf. Loosely cover pan with damp cloth or plastic wrap and allow to rise until doubled in size, 1 to 1-1/2 hours; dough should rise about 1/2 to 3/4 inch above edge of loaf pan.
Brush loaf with egg wash; using a sharp knife, cut 3-4 deep diagonal slashes on top of loaf. Cover with nonstick foil and place in preheated 400° oven; bake 15 minutes. Reduce heat to 375° bake 20 minutes. Remove foil; bake until loaf is deep golden brown and reaches an internal temperature of 200° when measured with an instant-read thermometer, about 10 minutes longer. Remove from oven; allow to cool 10 minutes. Remove loaf from pan. Cool completely on wire rack.
