Make the tangzhong: Stir together bread flour and water in a small saucepan over medium heat until flour is dissolved and mixture is smooth with no lumps. Continue stirring until mixture thickens and reaches 150 degrees Fahrenheit (about 10 minutes). Remove from heat, transfer to a mixing bowl, and cover.
In another mixing bowl, whisk together flour, sugar, instant yeast, and sea salt then make a well in the middle of the bowl.
Pour the tangzhong, warm milk, and melted butter into the well and mix with kitchen spoon until a tacky dough forms.
Turn dough out of the bowl onto a floured surface then knead it for about 10 minutes or until dough is soft and elastic and easy to stretch.
Shape dough into a ball and place back into mixing bowl then cover with a damp towel and set aside in a warm spot to rest and rise. Meanwhile, grease and flour loaf pan.
Once the dough has roughly doubled in size (after about one hour), punch/press the middle of the dough to flatten out air and turn out onto floured surface.
Separate dough into three or four equal pieces then roll each piece into a ball and place into prepared loaf pan.
Cover pan with damp towel and allow to proof until doubled in size (about 40 minutes). Preheat oven to 375 degrees farenheit.
Uncover pan then place on center oven rack and bake for 45 minutes or until golden brown and cooked through. When done, the bread should have a firm texture and register about 190 degrees Farenheit on a food thermometer inserted into the center of the loaf.