In a small saucepan, mix the 1/3 cup all purpose flour, water together and whisk until no lumps. Heat over medium (stirring constantly). Once mixture begins to thicken, temperature reaches 150F, remove it from the stove to, let it cool.
In a medium bowl, combine yeast with the warm milk, mix well and let sit for 10 mins. Add tangzhong mixture (cooked flour) and yeast mixture into bread flour mixture.