Add the warm water and active dry yeast to the bowl of a stand mixer. Add the vegetable oil and sugar. Stir briefly and let the mixture stand for 5 minutes, until foamy.

Add the beaten egg, salt, and 3 cups of flour. Using the dough hook, knead on medium-low speed for 3 to 5 minutes, until the dough is smooth and elastic. If it is still too sticky, add the remaining flour a tablespoon at a time until the dough is soft and workable.

Transfer the dough to a clean work surface. Divide it into 8 equal pieces and shape each piece into a smooth ball. There is no need for a traditional first rise.

Arrange the dough balls on a parchment-lined baking sheet, leaving space between each one. Cover loosely with a clean kitchen towel and let rest for 10 minutes. During this time, preheat the oven to 425°F.

Whisk the egg yolk with 1 tablespoon of water. Brush the tops of the rested buns with the egg wash, then sprinkle generously with sesame seeds.

Bake on the center rack for 8 to 12 minutes, until the buns are puffed and golden brown.

Transfer the buns to a wire rack and let cool before slicing.