Dissolve the yeast in water for 5-10 minutes.
Whisk together the flour, sugar and salt in a large bowl. Make a well in the center and add 3 eggs and oil. Whisk the eggs, pulling a little bit of flour into the center to make a paste.
Pour the yeast mixture into the well. Stir with a wooden spoon until combined. The dough will be shaggy.
Preheat oven to 200 degrees.
Dump the dough onto a floured surface and knead for 8-10 minutes. (Alternatively, put the dough into the bowl of a stand mixer fitted with a dough hook and knead on low speed, 8-10 minutes). The dough will be soft and smooth.
Turn off the oven. Place dough in an oiled bowl and cover with a kitchen towel. Place into the warm oven for 1-2 hours, until doubled in size.
Punch the dough down and divide into 3 equal pieces. Roll each piece into a rope 16-18 inches long. Line the ropes up next to each other on a baking sheet lined with parchment paper. Pinch the ends together on one side. Braid the dough. Dust with flour, cover with a kitchen towel and let rise for 1 hour.
Preheat oven to 350 degrees. Beat the remaining egg with 1 Tbsp. of water. Brush the dough with the egg wash. Bake 15 minutes. Rotate the baking sheet and bake another 20 minutes. Allow challah to cool on the baking sheet before slicing.