In a small bowl, combine the warm water (1 cup plus 2 tablespoons) and active dry yeast. Let it sit for about 5 minutes until frothy.
In a large mixing bowl, whisk together vegetable oil, sugar, beaten egg, and salt. Add the yeast mixture and stir until well combined.
Gradually add the all-purpose flour, starting with 3 cups, mixing until the dough comes together. Add more flour as needed up to 3-1/2 cups.
Turn dough onto a floured surface and knead about 5 minutes until smooth and elastic. Alternatively, knead with a stand mixer dough hook on medium speed for 5 minutes.
Place dough in a lightly greased bowl and cover with a kitchen towel. Let rise in a warm area for about 15 minutes, or until doubled in size.
Punch down dough to release air. Divide into 8 equal pieces and shape each into a ball. Place on a baking sheet lined with parchment paper, spaced apart.
In a small bowl, mix egg yolk and 1 tablespoon water. Brush mixture over tops of buns for a golden finish.
Optionally, sprinkle sesame seeds on top of the buns after brushing the egg wash.
Preheat oven to 375°F (190°C). Bake buns for 15-20 minutes until golden brown and hollow sounding when tapped.
Remove buns from oven and cool on a wire rack for a few minutes before serving.