Pour the warm water into a small bowl. Sprinkle the yeast and sugar over the surface of the water. Stir to dissolve and let stand at room temperature until foamy, about 10 minutes.
Combine caraway seeds and fennel seeds in a spice grinder and coarsely grind until no longer whole, but still slightly chunky (you can use a mortar and pestle for this, but I use an old coffee grinder). In a large bowl using a whisk or in the work bowl of a heavy-duty electric mixer fitted with the paddle attachment, combine the butter, molasses, instant espresso powder, salt, caraway seeds, fennel seeds, bran, cocoa powder, and rye flour. Mix until smooth and add yeast mixture. Beat for about 3 minutes. Add the unbleached flour, 1/2 cup at a time, and continue to beat (with paddle attachment if using a machine, or with a wooden spoon if mixing by hand) until too stiff to stir.
Turn the dough out onto a lightly floured work surface and knead until smooth, elastic, and no longer sticky, about 5 minutes, dusting with flour only 1 tablespoon at a time as needed to prevent sticking.
If kneading by machine, switch from the paddle to the dough hook and knead for 4 to 5 minutes, or until the dough is smooth and springy and springs back when pressed. If desired, transfer the dough to a floured surface and knead briefly by hand.
Place the dough in a greased bowl. Turn once to grease the top and cover with plastic wrap. Let rise at room temperature until doubled in bulk, 1 to 1 1/2 hours.
Gently deflate the dough. Turn the dough out onto a lightly floured work surface. Grease or parchment-line a baking sheet and sprinkle with cornmeal, if desired. Divide the dough into 12 equal portions. Shape each dough portion into a round ball and place seam side down on the baking sheet. Flatted each ball with your palm. Cover loosely with plastic wrap and let rise until doubled in bulk and puffy, about 25 minutes.
Twenty minutes before baking, preheat the oven to 375 degrees F. Place the baking sheet on the center lower rack in the oven and bake for 35-40 minutes, or until slightly browned and firm to the touch. Transfer to a rack to cool.