Feed your starter

• About 12 hours before you plan to begin to make the dough, feed your starter. I like to do this around 8pm so my starter is active in the morning. To a clean jar, add 50 grams of starter, 50 grams of bread flour and 50 grams of filtered water. Mix well and set on the counter until morning
  50 grams sourdough starter, 50 grams filtered water, 50 grams bread flour

Levain

• Add 50g of active sourdough starter, water, and flour to a bowl. Mix until combined, cover, and rest in a warm spot for 4 hours or until the levain has doubled in size. I like to place the covered bowl in the cool oven with just the light on. To measure when the levain has doubled in size, place a rubber band around the outside of the bowl (a glass or clear plastic bowl is useful here), marking the top of the levain mixture. This way, you can easily see when it’s double its size
  50 grams active sourdough starter, 50 grams filtered water, 50 grams bread flour

Challah Dough

Make Flour Paste:

• Once the levain has just about doubled in size, make the flour paste. Whisk water and flour in a small bowl until no lumps remain
  ½ cup water, 3 tablespoons bread flour
• Microwave, whisking every 20 seconds, until mixture thickens to a stiff, smooth, pudding-like consistency that forms a mound when dropped from the end of a whisk into the bowl, about 40 to 80 seconds. Alternatively, place the flour and water in a small saucepan and place over low heat. Whisk constantly until a thick paste forms

Make the Dough:

• In the bowl of a stand mixer, whisk together the water and levain. Add the flour paste, vegetable oil, egg and egg yolks. Whisk well until combined
  ¼ cup water, 100 grams levain, flour paste, 2 tablespoons vegetable oil, 1 large egg, 2 large egg yolks
• Add the flour. Fit mixer with dough hook and mix on low speed until all flour is moistened, 3 to 4 minutes. Cover with a clean towel and let stand for 20 minutes to allow the flour to hydrate (absorb the water) and to allow the gluten to relax
  2 ¾ cups bread flour
• After 20 minutes, remove the towel and add the sugar and salt to the bowl. Knead on medium speed for 9 minutes. Dough should be wrapped around the dough hook without sticking to the bottom or sides of the bowl. If the dough is sticking, add more flour, 1 tablespoon at a time, up to ¼ cup more, allowing the flour to fully incorporate before adding more
  ¼ cup granulated sugar, 1 teaspoon kosher salt
• Transfer the dough to a clean counter and lightly coat the now-empty mixing bowl with vegetable oil. Form the dough into a ball and return it to the oiled bowl, turning to coat all sides lightly in oil. Cover the bowl with plastic wrap. Let the dough rise until about doubled in volume, about 5 hours
• After the dough has doubled in size, place in the fridge overnight, 10-12 hours

Shape the Dough:

• Line a rimmed baking sheet with parchment paper and stack on top of a second rimmed baking sheet to prevent the bottom of the bread from getting too browned or burnt. Set on your counter next to where you'll be shaping the dough
• Remove the dough from the bowl onto a clean counter. Do not flour the work surface. Press the dough into an 8-inch square, expelling as much air as possible
• Using a bench scraper or sharp knife, cut the dough into 3 equal sized pieces. Working with one piece at a time, press or roll using a rolling pin until about ½ inch thick. With the long edge facing you, roll up into a roulade, pinching the edge to seal
• Roll against the counter to smooth the edge, applying more pressure on the ends to taper them. Roll until the rope is about 16-18 inches long. If the dough shrinks or resists stretching, cover it loosely with plastic wrap and let it rest for a couple of minutes. Repeat with remaining pieces of dough
• Arrange the 3 ropes so they are parallel, about an inch apart. Join the tapered ends together at the top and press to seal them together
• Braid the dough by taking the rope farthest on the left and passing it over the middle rope. Next, take the rope farthest on the right and pass it over the middle rope. Continue this process until there is no more dough to braid. Press the 3 ends of the braid together to seal
• Starting at the top of the braid, curl the dough inward, like a snail. You are essentially curling the dough into itself to create the round shape. Continue curling the braid around itself until you reach the end. Tuck the end underneath the loaf to seal
• Cover loosely with plastic wrap and let the dough rise 4-6 hours or until the challah has puffed up. To test if it’s done proofing, gently poke your pointer finger in the dough. If it bounces back right away, it’s not quite there. If it bounces back slowly, it’s ready

Make the Egg Wash:

• Preheat the oven to 350º F. Whisk together egg (or reserved egg whites) and salt. Brush the loaf with egg wash and sprinkle with sesame seeds, poppy seeds, or everything bagel seasoning, if using
  1 large egg , pinch kosher salt, 1 tablespoon sesame seeds
• Bake until the loaf is a deep golden brown and registers at least 195º F, 25 to 35 minutes. If the top is browning too much, but the bread is not yet done baking, tent a piece of foil over top to prevent it from over browning. Let the loaf cool on the baking sheet for 20 minutes. Transfer baked loaf to a wire rack and let cool completely before slicing, about 2 hours