Steps

make a Tangzhong

add all the dry ingredients to a bowl and mix together. Mix the tangzhong, egg, and water together and add to the dry ingredients. Mix everything and knead until you have a shaggy dough

add room temperature butter and continue to knead until the dough is smooth but slightly tacky. We add the butter later because butter can coat the flour and inhibit gluten formation

shape the dough into a taut ball and place in a greased bowl. Cover with a damp towel and let it proof in a warm place until the dough has doubled in size ~1 hr

deflate the dough by pressing down on it, cut it into thirds, and roll into 3 taut balls. Let the dough rest for 10-15 minutes covered by a damp towel

roll out each ball of dough into a flat sheet and fold into thirds vertically to make a long folded sheet of dough. Roll out the dough towards you and pinch the ends into the dough to secure tightly

place all 3 rolls of dough into a greased loaf pan with the stitched end side down and cover with a damp towel for second proofing. It should take anywhere from 40 minutes to an hour for the rolls to expand to the height of the loaf pan and cover all gaps.

bake the loaf at 350°F until he bread is golden brown and has a hard crust ~35 mins. Let the bread cool on a rack so that the bread doesn't continue to steam itself