Combine all of the ingredients for the buns in the bowl of a stand mixer fitted with the dough hook attachment. Beat the ingredients at high speed for 2 minutes until they begin to come together around the dough hook.
Lightly grease a large bowl with vegetable oil. Gather the dough into a ball and transfer it to the bowl. Cover the bowl with plastic wrap and allow the dough to rise in a warm, dark place for 60 to 90 minutes until it has visibly puffed.
Line a baking sheet with parchment paper. Gently deflate the dough and divide it into 6 equal pieces for regular-sized buns or 12 equal pieces for slider-sized buns.
Shape the dough pieces into balls, tucking the edges under to make smooth tops, and then place them on the baking sheet, spacing them apart so they do not touch. Gently flatten the balls so they're about 3 1/2 inches wide for regular-sized buns or 2 inches wide for slider-sized buns. Cover the baking sheet with plastic wrap and let the dough rise for an additional 60 to 90 minutes until the buns are noticeably puffy.
Place the rack in the center of the oven and preheat it to 350°F. Whisk the egg white with 2 teaspoons of water. Brush the tops of the buns with the egg white mixture and then sprinkle the buns with the sesame seeds (optional).
Bake the buns for about 20 minutes, until they're light, golden brown.
Remove the buns from the oven, transfer them to a rack and allow them to cool completely.
The amount of water used in the recipe depends on how humid your environment is. Use 2/3 cup water in summer months or more humid climates and use 3/4 cup water in winter months or in drier climates.
The egg white wash isn't essential, but it's what gives the buns their attractive sheen and golden brown crowns.
The buns can be stored in an air-tight container at room temperature.