Add yeast and sugar to warm water in a small bowl. Stir to combine and allow it to sit for 5-10 minutes to activate the yeast.
Pour activated yeast water into the bowl of a stand mixer.
Add the oil and salt along with 2 cups of the flour.
Using a dough hook combine the ingredients on low speed until combined.
Continue adding two cups of flour at a time until all the flour is incorporated into a sticky dough.
Increase the speed of the mixer to medium and knead the dough for 6 minutes or until you have a smooth, elastic dough.
Remove the dough from the bowl and form it into a ball with your hands. Place ball of dough into a lightly oiled bowl.
Cover loosely and allow dough to rise, until doubled in size, about 1-1½ hours.
Punch down the dough and cover it. Allow dough to rise for 45 minutes to an hour.
Divide dough into 12 equal sized pieces.
Roll each piece of dough into a round ball.
Flatten slightly forming the balls into a disc shape and place on a baking sheet.
Allow the buns to rest for 30 minutes.
Preheat oven to 350℉.
In a small bowl whisk together the egg and water.
Right before placing the buns in the oven, brush the tops of them with the egg wash.
Sprinkle the buns with sesame seeds.
Bake buns for 20-25 minutes or until they are a rich golden brown.
Remove from the oven and transfer buns to a wire rack. Allow them to cool to room temperature before slicing them in half.