In a large mixing bowl or the bowl of a stand mixer fitted with a dough hook, stir together the warm water, sugar, and yeast. Let stand until foamy, about 5 minutes.

Add 4 cups flour, oil, eggs, egg yolk, and salt. Mix on medium-low speed until a sticky and elastic dough, 8 to 10 minutes. It should cling to the bottom of the bowl but be pulling away from the sides and making a slapping sound. Add additional flour a tablespoon at a time as needed after 6 minutes.

Shape the dough into a ball. Place in a lightly oiled large bowl and turn the dough to coat. Cover and let rise in a warm spot (about 75F) until doubled in size, 1 to 2 hours.

Turn out the dough onto a very lightly floured surface. Divide the dough into 6 equal pieces. Stretch and roll each piece into a 12-inch long rope. Place all 6 ropes parallel to each other, pinch the ends together, then fan the ropes out a bit.

To make the 6-strand braid, take the outside right rope and move it over 2 strands towards the center. Take the second-from-the-left strand and cross it over all of the strands, moving it to the outer right. Take the outer left strand and move it over 2 strands towards the center. Take the second-to the-right strand and move it to the outer left. Continue with this pattern until the full loaf is braided. Pinch the end and tuck both ends under just a bit. Place the braided loaf on a parchment paper-lined large baking sheet. Loosely cover and let rise until almost doubled in size, 30 minutes to 1 hour.

When almost finished rising, preheat the oven to 350F.

In a small bowl, beat the egg white until frothy. Brush the risen loaf with the egg wash and sprinkle with seeds, if desired.

Bake for 20 to 25 minutes or until the top is a deep golden brown. (You can also temp it with an instant-read thermometer- it should read between 195 and 205F.) Place the loaf on a wire rack and let cool completely. Challah is best enjoyed the day it’s baked, but it can be tightly wrapped in plastic or stored in an airtight container for a couple of days.