Step 1

Make the tangzhong by heating up milk in a small pot. Stir in bread flour until a thick paste forms. Pour paste into a medium bowl. Add 1/2 cup milk and beaten egg; mix well.

Step 2

Place flour and yeast in a large mixing bowl. Mix with a spatula or by hand. Pour in tangzhong mixture. Stir well with a spatula until no dry spots remain. Gather dough in the middle of the bowl. Cover with a damp towel. Let rest for 20 minutes.

Step 3

Add salt to the dough and knead until incorporated. Repeat with sugar, 1 tablespoon at a time. Knead until dough is smooth, about 10 minutes. Add butter; keep kneading until evenly incorporated and dough is smooth.

Step 4

Form dough into a ball and place into a well oiled bowl. Turn dough to grease on all sides. Let proof at room temperature until doubled, about 1 hour.

Step 5

Turn dough out onto a clean work surface and deflate it. Press gently into a rectangle; roll up into a cylinder and transfer to a loaf pan. Let loaf proof until doubled, about 1 hour.

Step 6

Preheat the oven to 375 degrees F (190 degrees C).

Step 7

Place loaf pan on the middle rack of the preheated oven and reduce oven temperature to 350 degrees F (175 degrees C). Bake until golden brown, 30 to 35 minutes. Cool for 5 minutes before inverting onto a cooling rack. Cool completely before slicing.