Add all dry ingredients bread flour, cake flour, milk powder, sugar, salt, yeast into the bowl. Stir until mix well with lower speed of the mixer.
Add water, fresh milk, egg, and cooking oil into the flour bowl. Then turn up the speed slightly and continue kneading until become very stretchy and tacky to touch. Add butter and kneading for 15-18 minutes.
Turn off the mixer and warp the dough with plastic or fabric at normal room temperature for 45-60 minutes (until the dough expand for double size)
Divide the dough into small pieces as 10 -15 grams/pcs. Shape each piece into a tight ball. Set aside for 40-50 minutes.