Place the yeast, water, and sugar in a bowl. Mix well.
Let it sit for around five minutes or until bubbles start forming on top.
Add the olive oil, one egg, and both the flours.
Knead the dough until it's soft.
Form a ball out of the dough, place it in a clean bowl, and cover it with a towel.
Place the bowl in a warm temperature area (around 77 degrees) and allow it to rise for an hour or until the dough has doubled in size.
Split the dough in half and then each half into three.
Roll out three pieces of dough at a time and attach them at the top.
Braid the challah by putting one string over the middle followed by the other string.
Repeat with the other piece of dough and place both challahs on a lined baking sheet. Cover with a towel and allow them to rise for another hour or until they double in size again.
Preheat the oven to 350 degrees. Whisk the second egg and brush it over the challahs. Sprinkle sesame seeds over the challahs and then bake for around 35 minutes or until golden brown.
Allow the challahs to cool completely.