Poppy Seed Challah

If using a bread machine:

Place all the ingredients in the pan according to the order in the manufacturer's instructions.
Set crust on medium; program for the Basic .
Press Start.
When the baking cycle ends, immediately remove the bread from the pan and place it on a rack. Let cool to room temperature before slicing.

To make a braided loaf, use the Dough cycle and follow Braiding steps.

If not using a bread machine:

Combine the flour with the rest of the dough ingredients. Mix and knead them by hand or mixer until you have a soft, smooth dough. If the dough is very sticky, add an additional 1/4 cup (30g) of flour.
Allow the dough to rise in a plastic wrap-covered bowl for about 2 hours, or until it's puffy; it won't necessarily double in bulk.

Gently deflate the dough.

Braiding the loaf:

Divide the dough into pieces, the number depending on what kind of braid you want to make. Roll each piece into a rope about 20" long. If the dough starts to shrink back as you roll, cover it and let it rest for about 10 minutes, then resume rolling. The short rest gives the gluten a chance to relax.

Braid the loaf.

Gently pick up the braided loaf, and place it on a lightly greased or parchment-lined baking sheet.

Cover the loaf with lightly greased plastic wrap and let it rise at room temperature until it's very puffy, 60 to 90 minutes. Toward the end of the rising time, place a rack in the upper third of your oven and preheat the oven to 375°F.

To make the topping: Whisk together the reserved egg white and water. Brush the mixture over the risen loaf. Sprinkle generously with poppy seeds or sesame seeds, if desired.

Bake the challah on the oven's upper rack for 25 to 30 minutes, or until it's a deep golden brown and a digital thermometer inserted into the center reads 190°F.

Remove the challah from the oven and transfer it to a rack to cool.