challah

Time: ~3 1/2 hours (1/2 hour working + 2 1/2 hours rising + 1/2 hour baking)

Yield: 1 loaf

Add the 1/2 Tbsp sugar to the water, and whisk to dissolve. Sprinkle the yeast over the water and whisk in. Let stand until you see a thin foamy layer on top, about 5 minutes. (Although proofing yeast is not really necessary these days?)
Whisk in oil. Beat in 2 eggs and yolk, one at a time. Mix in remaining sugar and salt. Gradually add flour. When dough holds together, it is ready for kneading.
Turn dough onto a floured work surface. Knead dough until smooth (5-10 minutes), adding flour as needed to get it tacky. The dough has finished kneading when it is soft, smooth, and holds a ball shape.

Place dough in greased bowl. Cover with plastic wrap, and let rise in a warm place for 1 hour, until almost doubled in size. (Can set oven to warm for a couple minutes while the yeast proofs, then turn off.)
Punch down dough, cover and let rise again in a warm place for another 30 minutes.

Punch down the dough again, turn out, and separate into 6 equal pieces.
Roll each piece of dough into a long rope roughly 1-inch thick and 16 inches long. If the ropes shrink as you try to roll them, let them rest for 5-10 minutes to relax the gluten and then try again.
Watch this video to make a 6-braid challah. (I could try to describe it here, but even with pictures this is confusing.)
Place braided loaf on a baking sheet lined with parchment.

Whisk remaining egg white with 1 Tbsp water and brush it on loaf. Either freeze or let rise another hour in the refrigerator.

Place a tray of water (about 4 cups) on the lowest rack before preheating. (Put the empty tray in first, then add water, to avoid sloshing water out of the tray.)
Set a rack in the middle of the oven, and preheat to 375°F. Brush loaves with the egg white glaze again. Sprinkle bread with seeds, if using. (If freezing, remove from freezer 5 hours before baking.)
If not using steam, place the baking sheet atop another baking sheet (to insulate the bottom crust, and keep it from browning too much).
Bake for 30-40 minutes, rotating halfway through. Once it hits deep golden brown, can tent loosely with aluminum foil. Bread is done when it registers 190°F in the center.
Cool loaf on a rack.

Notes

This uses about 1% yeast, which seems to be standard for dry yeast. Could also try this with fresh yeast, if I can find where to buy it.

Baking with steam in the oven gives a nice crust without drying out the crumb, and prevents overbrowning the bottom.

Adapted from many other recipes:

Can also braid the bread in something other than 6 parts - see https://www.youtube.com/watch?v=RP6j7esQyjk