Lightly oil a 4 quart food storage container. Set aside.
Place the flours, yeast, and salt in the bowl of a stand mixer and whisk lightly to combine.
Place on the mixer fitted with the paddle attachment. Add the water, butter, egg, and honey, and stir just until combined.
Replace the paddle attachment with the dough hook and turn on low speed, kneading until the dough is smooth and pulls away from the sides.
Place the dough into the oiled container, seal with the lid, and place in a warm spot to rise for 1 hour or until doubled in size.
Once the dough has risen, remove from the container using a bench scraper and place on the counter or work surface — no flour is required. Divide the dough into 8 equal portions and form into slightly flattened discs and place on a lightly oiled rimmed baking sheet.
Cover with plastic and allow the dough to rise 30-40 minutes, or until nice and puffy.
Preheat the oven to 375 degrees F and prepare the egg wash. Place the egg yolk and 2 teaspoons of water in a small bowl and mix until incorporated.
Remove the plastic from the buns and brush each bun with the egg wash by tapping a light coating evenly over the top. You will not need all of the egg wash.
Sprinkle on the sesame seeds, if using, and bake in the oven for 12-15 minutes or until the buns are golden brown.
Cool on a wire rack, and when they've cooled, split using a serrated knife.