Dissolve the yeast in warm water for 5-10 minutes.
Whisk together the flour, sugar and salt in a large mixing 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 bread 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 for the first rise. 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: Cross the center rope over the rope on the right. Then, cross the center rope over the rope on the left. Continue crossing center over right, center over left, until the dough is braided. Tuck the ends under.
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 in a small bowl. Brush the entire loaf with the egg wash.
Bake 15 minutes. Rotate the baking sheet and bake another 20 minutes. Allow challah to cool to room temperature on the sheet pan before slicing.