Makes: 1 loaf (12 slices) for $1.87. Prep: 45 minutes. Rise: 3 hours. Bake: at 350° for 30 to 35 minutes.
Mix 1/3 cup warm water and sugar in small bowl. Sprinkle yeast over top. Let stand until foamy, 5 to 10 minutes.
Mix bread and rye flours, salt and caraway seeds in large bowl. Whisk in espresso and cocoa powders. Add vinegar and molasses to remaining 1/3 cup warm water. Stir vinegar-yeast mixture into flour mixture in bowl. Add more bread flour if dough is too sticky.
Turn dough out onto floured work surface. With floured hands, knead until smooth and elastic, about 10 minutes; dough will be slightly stiff.
Transfer dough to greased bowl; turn to coat. Cover with clean kitchen towel or plastic wrap. Let rise in warm place until doubled in volume, about 1-1/2 hours.
Prepare dough, following steps 1 through 3, omitting espresso and cocoa powders. Transfer to a second greased bowl, turning to coat. Cover with towel. Let rise in a warm place until doubled in volume, about 1-1/4 hours.
Remove doughs from bowls. Punch doughs down. Let rest for 5 minutes. Roll doughs into 11 x 8-inch rectangles. On top of rye dough, place pumpernickel dough, overlapping so 1-inch strip of rye dough is exposed along short side. Fold exposed lip over; firmly roll up doughs together. Pinch seams to close; turn ends under. Transfer to greased 8 1/2 x 4 1/2 x 2 5/8-inch loaf pan. Cover with kitchen towel. Let rise until doubled, about 1-1/2 hours.
Heat oven to 350 degrees F. Lightly brush top of risen loaf with the beaten egg white. Sprinkle with the caraway seeds. Bake in heated 350 degree F oven for 30 to 35 minutes or until golden, puffed and hollow-sounding when tapped. Remove from pan to wire rack to cool.