Make Tangzhong: Cook flour and milk mixture until thickened. Cool completely.
Mix Dry Ingredients: Combine flour, yeast, sugar, salt, and milk powder.
Combine Wet Ingredients: Mix tangzhong, egg, and warm milk.
Form Dough: Combine wet and dry ingredients until shaggy dough forms.
Knead: Knead 8-10 minutes until smooth and elastic.
Add Butter: Work in softened butter until fully incorporated.
First Rise: Rise 1-1.5 hours until doubled.
Shape: Divide into 3 pieces, shape, and place in loaf pan.
Second Rise: Rise 45-60 minutes until crowning pan.
Bake: Brush with egg wash, bake at 350°F for 30-35 minutes.
Cool: Cool in pan 5 minutes, then on wire rack.