Prepare the yeast. Place the lukewarm water, yeast, and a pinch of sugar in a small bowl. Stir to combine and cover with a plate or a lid. Set aside for 10 minutes or until the yeast is foamy.
Mix the dry ingredients. In a large bowl, whisk together the sugar, flour, and salt.
Add the liquid. Make a well in the center of the flour mixture. Pour in the yeast mixture, and add eggs, egg yolk, and oil.
Mix and knead. Mix everything with a spatula, then knead the dough by hand for 10 minutes or mix it in a stand mixer with a dough hook attachment for 6-8 minutes, or until smooth.
Rise. Lightly coat a large bowl with oil, then place the dough in the bowl. Cover it with a clean towel and let the challah rise for 2 hours or until doubled in size.
Prep the dough. Uncover and punch down the dough to remove air. Turn the dough out onto a lightly floured surface and divide it into three equal portions. I use a kitchen scale to make sure they’re even.
Shape the dough. Roll each portion into a 15 to 16-inch-long rope. Arrange the ropes vertically, one next to the other, then gather and squeeze them at the top.
Braid the dough. Braid the ropes together just like you would braid hair. Line a baking sheet with parchment paper and then transfer the bread onto the baking sheet.
Second rise. Dust the bread with some flour and cover with a clean kitchen towel or cloth. Let it rise for 45 minutes.
Prepare to bake. Meanwhile, preheat your oven to 350°F.
Make the egg wash. Whisk the reserved egg white with water until combined.
Bake. Brush the dough with the egg wash, then transfer the bread to the oven. Bake for 30-35 minutes, rotating halfway through.
Cool and serve. Remove the challah bread from the oven and cool it on a wire rack before slicing and serving.
Notes
The yeast needs to be fresh for a perfect challah bread. If the yeast is not foamy, discard it and try with a new packet.
For the perfect kosher bread, make sure to check the egg yolks. They mustn't have any blood spots.
Do not substitute water with milk.
The dough should be smooth. If the dough is sticky halfway through kneading, add some extra flour.