Combine milk and butter in a saucepan and heat to 100 degrees F. If the milk is hotter than 100 degrees F let it cool before proceeding, so you don't kill the yeast. Pour the warm milk into the bowl of a stand mixer. Add yeast to the mixing bowl and stir briefly, just to dissolve the yeast.
Add the sugar, egg, flour, and salt to the mixing bowl. With the paddle attachment, mix the ingredients on medium-low speed until completely combined, about 2 minutes. The dough will be rough looking, but it should stick together when pressed. It should be tacky, but not overly sticky. You may need to add a little extra flour if the dough is too sticky to handle. Turn out dough into an oiled bowl and cover with plastic wrap. Place in warm spot and let rise until doubled in size, about one to two hours.
Using a kitchen scale, cut off 2-ounce pieces of dough and form them into balls. Place the balls of dough in the oiled bowl and cover with a damp towel. One at a time, remove the balls and roll them out flat with a rolling pin into an oval shape. Brush the tops of the dough lightly with oil and then fold in half. Place each bun on a small square of parchment paper. Arrange the buns on a large tray, loosely cover with plastic wrap, and let rise for another 15-20 minutes. During the second rise, prepare a wooden or metal steamer by filling the bottom portion with water. Arrange buns in the steamer so they are not touching, cover, and steam for 5 minutes. You may need to adjust the time depending on your particular steamer. Open one bun to test it. If the inside is still raw, steam for a little longer. If the top surfaces of the buns are wrinkled, then they have steamed for too long. Reduce the time for the next batch. Serve buns immediately or store in the refrigerator and re-steam to serve. Fresh is best!