- To make the starter: Combine all of the starter ingredients, mixing just until a cohesive dough forms. Allow it to rest, covered, for 12 to 16 hours at room temperature. When the starter is ready, it will be filled with large holes and bubbles.
- To make the dough: Add the water to the starter, and mix until smooth.
- Add the flour, yeast and salt, and knead the dough until it's fairly smooth but not necessarily elastic, about 3 minutes by machine, or 5 minutes by hand. (The gluten will continue to develop as the dough rises, so you don't want to develop it fully during the kneading process.)
- Place the dough in a lightly greased bowl, cover, and allow the dough to rise at room temperature for 1 1/2 hours. To help develop the gluten and distribute the yeast's food, turn the dough twice during the rising time: gently fold all four sides into the middle, and turn the dough over.
- Divide the dough in thirds, and roll each third into a 20"-long rope. Braid the ropes.
- Set the braid on a lightly greased or parchment-lined baking sheet, cover with greased plastic wrap and let rise 1 to 1 1/2 hours, until just puffy.
- To bake the bread: Preheat oven to 425°F. Gently brush the braid with the beaten egg white mixture and sprinkle generously with sesame seeds.
- Bake at 425°F for 25 to 35 minutes or until the loaf is golden and feels lighter when picked up. Remove the braid from the oven and cool on a rack.
- Store on the counter, well-wrapped, for 3 days, or freeze for up to 3 months.