• Combine the sourdough starter, water and rye flour. Cover the bowl and let it ferment about 3-4 hours at room temperature (you can do this the night before and continue making the dough in the morning).

Make the light dough

• Combine 4 oz (1/2 cup) of the starter, 6 oz warm water, 2 ½ oz rye flour and ½ cup of the bread flour in a mixer bowl. Mix until a thick batter is formed.
• If you're using a stand mixer, switch to the dough hook. Add ½ oz barley malt syrup, 1 teaspoon table salt and the remaining bread flour. If the dough is extremely sticky sprinkle in a few more tablespoons of bread flour.
• Knead the dough on medium for 5 minutes until it begins to clear the sides of the bowl and forms a ball around the hook. Turn it out onto a lightly floured surface. If working by hand, stir in as much of the flour as you can then turn the dough out onto a floured surface and knead for 4-5 minutes.
• The dough may be a little sticky so keep your hands well floured. Place the dough into a lightly oiled bowl, turning once to coat the dough.
• Place the dough into an oiled bowl, turning once to coat. Cover and set at room temperature for 1 hour. After an hour, working from four corners of the dough (still in the bowl) use your hand to lift the top edge of the dough over into the middle of the dough. Repeat with the other 3 sides then flip the dough over. Cover and set at room temperature for another hour. Repeat the folding procedure 2 more times so the dough rises for a total of 3 hours. By now the dough should be lively, elastic and airy. If the dough is still sluggish give it another hour or two at room temperature. After the initial fermentation the dough can be refrigerated for up to 2 days before baking or you can go ahead and shape and bake the loaf.

Make the dark dough

• Combine the rest of the starter, 6 oz brewed coffee, 2 ½ oz rye flour, 1 tablespoon cocoa powder and ½ cup of the bread flour in a mixer bowl. Mix until a thick batter is formed.
• If you're using a stand mixer, switch to the dough hook. Add ½ oz barley malt syrup, 1 teaspoon table salt and the remaining bread flour. If the dough is extremely sticky sprinkle in a few more tablespoons of bread flour.
• Knead the dough on medium for 5 minutes until it begins to clear the sides of the bowl and forms a ball around the hook. Turn it out onto a lightly floured surface. If working by hand, stir in as much of the flour as you can then turn the dough out onto a floured surface and knead for 4-5 minutes.
• The dough may be a little sticky so keep your hands well floured. Place the dough into a lightly oiled bowl, turning once to coat the dough.
• Place the dough into an oiled bowl, turning once to coat. Cover and set at room temperature for 1 hour. After an hour, working from four corners of the dough (still in the bowl) use your hand to lift the top edge of the dough over into the middle of the dough. Repeat with the other 3 sides then flip the dough over. Cover and set at room temperature for another hour. Repeat the folding procedure 2 more times so the dough rises for a total of 3 hours. By now the dough should be lively, elastic and airy. If the dough is still sluggish give it another hour or two at room temperature. After the initial fermentation the dough can be refrigerated for up to 2 days before baking or you can go ahead and shape and bake the loaf.

Assemble and bake

• Turn the light dough out onto a lightly floured surface. Roll the dough into a 8" x 10" oval. Do the same with the dark dough.
• Lay the dark dough on top of the light dough then roll the dough from the long side to form a tight log. Place the loaf on a wooden peel or sheet pan sprinkled liberally with corn meal.
• Cover with plastic wrap and leave in a warm place until doubled in size, and it springs back slowly when poked, about 2-3 hours. Alternately, you can refrigerate the loaf overnight and rise and bake the next day.
• Preheat the oven to 400 °F. If you have a baking stone place it in the oven to preheat. Make 5 diagonal slashes in the dough with a single edge razor or very sharp knife. Brush the dough with egg white and sprinkle with caraway seeds, if desired. Slide the dough onto the preheated stone or slide the sheet pan into the oven.
• The bread is ready when the internal temperature of the loaf is 200 °F. Baking time is approximately 30 minutes.
• Cool completely on a wire rack before slicing.