Step three: While the dough is rising, make the wash
Put the flour in a medium deep bowl and add the boiling water in a slow stream, whisking. Then continue to whisk to eliminate as many lumps as possible. Let cool completely, then beat in the egg and set aside.
One hour before baking, place a baking stone or heavy baking sheet on the middle oven rack and heat the oven to 425°F.
Step five: To shape the bread
Turn the dough out onto a lightly floured surface. Divide it in half and form each half into a loose ball. Let the dough relax for 15 minutes, covered with plastic wrap, an upturned bowl, or a damp towel.
Gently pat each ball of dough into a disk 6 to 7 inches in diameter and about 1 inch thick. Cover again and allow to relax for another 15 minutes.
Whisk the wash again to mix. It should be the consistency of heavy cream; if it is too thick, add room-temperature water a tablespoon at a time, whisking, to achieve the right consistency. Pour the wash into a shallow bowl or lipped plate big enough for you to dip your spread hand into.
Liberally dust a baker’s peel or upside-down baking sheet with bran or whole wheat flour. Transfer one of the disks to the peel or sheet. Dip your palms and fingers in the wash and gently pat the disk out to a circle about ¾ inch thick, washing its surface as you go.
To score the bread, dip the sides of your hands in the wash and use them to score the outer edge of the dough in an approximate circle, leaving a ½-to ¾-inch-wide border: Start by positioning your hands at opposite sides of the dough, palms facing each other. As you push the sides of your hands into the bread to score it, gently move them outward to stretch the dough ½ inch or so. The dough will now be a rough oval. Then work your way around the bread, dipping your hands in the wash as needed to keep them from sticking, until the dough is roughly circular again. Don’t worry about creating a perfect scored circle, but do be sure that the scores join to make a continuous line around the edge of the bread. When you’re finished, the bread should be 8½ or 9 inches in diameter.
Now dip your fingertips in the wash and place your hands side by side on the dough, about 1 inch from the circular score along the bottom edge of the dough. Push your fingers deeply into the dough (don’t tear it) and then repeat, moving your hands apart to create a score in a single line that does not extend beyond the outer scored border. Repeat to create parallel scores about an inch apart on the dough, dipping your fingers in the wash as needed. Then use the same technique to create roughly parallel cross-hatch scores at approximately 45 degrees to the first set. Your scores needn’t be perfect, but they should be deep—fingerprints clearly visible—or they’ll disappear as the bread bakes.
Sprinkle the loaf with half the sesame or nigella seeds, if using, and slide onto the baking stone or preheated baking sheet. Bake until golden with pale spots, 25 to 30 minutes, rotating it once at the halfway point. Transfer to a wire rack to cool, or serve hot after allowing the bread to rest for a few minutes. Brush the excess bran or flour from the bottom of the loaf with a kitchen towel or stiff brush after it has cooled for a few minutes, if you wish. Repeat the shaping and baking with the remaining dough.