1) To make the dough: Combine all of the dough ingredients except the raisins, and mix and knead them, by hand, mixer, or bread machine, until you have a soft, fairly smooth dough.
2) Allow the dough to rise, in a lightly greased, covered bowl, for 2 hours, or until it's puffy though probably not doubled in bulk.
3) Gently deflate the dough, and knead in the raisins.
4) Lightly grease a 9" round cake pan.
5) Roll the dough into a 30" to 36" rope. If it shrinks back, walk away and leave it alone for 10 minutes, then resume rolling. The longer the rope the more distinct the spiral, but if it isn't exactly 36" long, don't stress; just get as close as you can.
6) Coil the rope into the prepared pan, starting in the center.
7) Cover the challah gently with lightly greased plastic wrap or a proof cover, and allow it to rise for about 60 to 90 minutes, until it's puffy and pretty much fills the pan.
8) Near the end of the bread's rise, preheat the oven to 375°F.
9) Whisk together the egg and water. Brush the risen dough with the egg mixture. Sprinkle with coarse white sugar, if desired.
10) Bake the bread for 20 minutes, tent it with foil and bake for an additional 15 to 20 minutes, until it's a deep, golden brown, and an instant-read thermometer inserted into the center registers 190°F.
11) Remove the bread from the oven, and after a minute or so carefully transfer it to a rack. Cool the bread to lukewarm before cutting it.