Combine dry ingredients
Beat egg yolks
Add tangzhong to egg yolks, then add dry ingredients, including yeast
Add the milk alternately with butter, 1 tablespoon at a time, letting each tablespoon fully incorporate into the dough before adding the next
Blend well. Knead until smooth, about 10 minutes on medium-high speed using the stand mixer
Cover the mixing bowl in plastic wrap and let the dough rise for 1 hour or until doubled in size
Cut the dough into 6 pieces and form into balls
Flatten each piece into a rectangle, then fold short ends in towards each other as if folding a letter. Flatten again and tightly roll into a log starting with the short end
Let dough rest for another hour until puffy and doubled in size
Brush egg wash on top of loaf
Bake in a well-greased loaf pan for 30 mins at 375F (or 190C) preheated oven until deeply golden on top
Let cool 5 minutes then turn loaves out onto a cooling rack. Let cool completely