1) To make the dough: Combine all of the dough ingredients and mix and knead them, by hand, mixer, or bread machine, until you have a soft, smooth dough.
2) Allow the dough to rise, covered, for about 2 hours, or until it's puffy and nearly doubled in bulk.
3) Gently deflate the dough, and transfer it to a lightly greased work surface.
4) You may braid the challah the traditional way, into a three-strand braid. For a fancier presentation, make a four-strand braid, as follows. Divide the dough into four pieces, and shape each piece into a rough 6" log. Cover the logs with lightly greased plastic wrap or a proof cover, and let rest for 10 minutes.
5) Roll each log into a 15" rope. Cover, and let rest for 10 minutes.
6) Continue rolling the ropes til they're about 20" long; they'll shrink back to about 18" as they sit.
7) Lay the strands parallel to one another, and pinch the ends on your left together.
8) Take the rope nearest you, and move it up over the two adjoining ropes.
9) Next, move the rope back under the rope next to it. Fan the ends of the ropes out again.
10) Repeat the process, but start with the rope farthest away from you. Bring it down and across the two adjoining ropes, and then back under the rope nearest it. Continue in this fashion, alternating which side you begin with, until you've braided the whole loaf. Pinch the loose ends together, and tuck them underneath the loaf.
11) Gently pick up the loaf, and place it on a lightly greased or parchment-lined baking sheet.
12) Cover the loaf with lightly greased plastic wrap or a proof cover, and let it rise till it's very puffy, 60 to 90 minutes. Towards the end of the rising time, preheat the oven to 375°F.
13) Whisk together the egg and 1 tablespoon water, and brush this glaze over the risen loaf.
14) Place the baking sheet atop another baking sheet; this will insulate the bread's bottom crust, and keep it from browning too much. Put the challah in the lower third of the oven, and bake it for 20 minutes.
15) Tent the challah loosely with aluminum foil, and bake for an additional 25 minutes, until the loaf is golden brown.
16) Remove the bread from the oven, and place it on a rack to cool.