In a small bowl, combine the yeast with the warm water. Add a large pinch of sugar. Stir to dissolve the yeast. Set aside for 10 minutes or so, until the yeast is activated forming a foamy layer.

In a large mixing bowl, combine the flour, egg yolks, sugar, salt, and oil. Mix with a wooden spoon.

Add the yeast mixture, and mix with the wooden spoon until the dough is too hard to mix. Transfer the dough to a lightly floured work surface, and knead by hand for 10 minutes. If the dough is too sticky as you knead, add a very little bit of flour and continue kneading until the dough is soft and smooth.

Place the dough in a large, lightly oiled mixing bowl. Cover with a kitchen cloth and keep it in a warm spot for 1 ½ until the dough rises (the dough is ready when it has doubled in size).

Punch the dough down and turn it back onto a lightly floured work surface. Divide the dough into three equal pieces, then roll each piece into a rope that's about 16 to18 inches long. Braid the three ropes together like you would hair. Squeeze both ends together to complete the braid.

Place the braided loaf on a large baking sheet lined with parchment paper. Cover and return to a warm spot for another 30 to 45 minutes allowing it to rise again. Meanwhile, preheat the oven to 350 degrees F.

Brush the loaf generously with about 2-3 tbsp of the egg whites you reserved earlier. Sprinkle the sesame seeds on top.

Bake in the 350 degrees F heated-oven for 20-25 minutes, or until golden brown. Let the challah bread cool before slicing.