Once dough has doubled, punch down the dough in the bowl to remove air pockets.
Sprinkle your work surface with the extra flour and turn the dough out onto it. Divide the dough into three equal pieces and roll each piece into a 13-16 inch long strand.
Place strands parallel to each other and close together on the prepared baking sheet. Separate them into two strands to the left, and one strand to the right.
Starting from the MIDDLE of the bunch of strands, begin braiding: Take the LEFT outer strand and cross it over so it’s between the two other strands, and rest it alongside the RIGHT strand. You should now have two strands on the RIGHT and only one strand on the LEFT.
Take the RIGHT outer strand and cross it over so it’s between the two other strands, and rest it alongside the LEFT strand. You should now have two strands on the LEFT (again) and only one strand on the right (AGAIN). (See video).
Repeat this process to the bottom of the bunch of strands, then pinch the ends together and tuck them under the braid.
Gently lift the braided dough off the baking sheet and INVERT it so the loose strands are now hanging down toward you and the braided part is pointing up.
Part, braid, pinch, and tuck the remaining strands using the method above. You should have a fully braided loaf when you’re done.
Cover the braided challah loaf with a clean tea towel and place in a warm place for its second rise, about 30 minutes, until the loaf has about doubled in size.