To get started we're going to make our Tangzhong. In a small sauce pan, add in your bread flour + water and cook it over low heat, stirring constantly to prevent the mixture from burning and clumping up.
Once the Tangzhong turns into a thick paste, remove it from the stove and transfer it to a small bowl or dish.
Cover it with plastic wrap and leave it in the fridge for at least 30 minutes to allow the Tangzhong to cool down.
Once the Tangzhong has cooled down, we're going to make our dough. In a large mixing bowl, add in your bread flour, sugar, salt, instant yeast, cinnamon powder, milk powder, 1 egg, and our Tangzhong from earlier.
Now using a stand mixer, give the dough mixture a quick few whisks then slowly add in your milk as well. I'm using the #2 speed on my stand mixer.
Continue mixing the dough for 3-4 minutes then add in your room temperature butter.
Then continue mixing the dough for an additional 9-10 minutes.
Once the dough becomes nice and smooth, transfer it to a large greased bowl, shape it into a round ball and cover it with plastic wrap or a towel and let it rise until double in size in a warm place (about 1 hour).
Now while the dough is proofing, we're going to prepare our raisins.
In a bowl, soak your raisins in hot water (do not use boiling hot water) for about 15 minutes.
Then drain the raisins and pat dry with a paper towel and set it aside.
When our dough has finished proofing, de-gase the dough by punching down on it, and then transfer it to a floured countertop.
Add some flour to the dough and then flatten it with your hands.
Next roll out the dough into a large rectangle.
Afterwards add about 1-2 handfuls of raisins to the dough and then roll out the dough from one end to the other to form a log.
Now shape the dough into a ball and then add some more raisins to it.
Once again, shape the dough into a ball and add some raisins to it.
Repeat this process until you've added in all of the raisins.
Once done, shape the dough into a round ball one more time and then weigh it out.
Next, divide the dough into 12 pieces and weigh out each piece to get equal portion sizes.
Now add some flour to your countertop and shape each piece of the dough into round balls by pulling the sides of the dough inwards with one hand while rotating the dough with the other hand.
Then pinch the ends of the dough to seal it and roll the dough in a circular motion using the palm of your hands on your countertop to get a nice round shape.
Place the buns onto a baking tray lined with parchment paper about 1 inch apart from one another.
Cover it with plastic wrap or a towel and let it rise for about 45 minutes in a warm place.
Once the buns have finished proofing, apply an egg wash to the top of the buns by beating an egg together with a splash of milk.
Finally, we're going to bake the buns in a preheated oven at 350°F (180°C) for about 18-20 minutes or until the top is golden brown.