Mix bread flour, sugar, and salt in a bowl.
Add milk, egg, dry yeast, and butter, then knead the dough.
Let the dough ferment for the first time for 1 hour.
Divide and shape the fermented dough into balls.
Wrap the dough around red bean paste filling.
Place in a bread tin and ferment for the second time for 40 minutes.
Bake in a preheated oven at 180°C for 20 minutes.