In a small sauce pan, add in your water & bread flour to make the Tangzhong. Heat this mixture well over low heat while constantly stirring it.
Cook the mixture until it becomes a thick viscous like substance. Then remove it from the stove and transfer it to a small bowl or dish. Cover it with plastic wrap and store it in the fridge for at least 20 minutes prior to using to cool the Tangzhong down before using.
Next in a large mixing bowl, add in your bread flour, sugar, salt, yeast, milk powder, egg, and the cooled down Tangzhong from earlier.
Using a stand mixer, give it a quick whisk then slowly add in your milk as well to the dough and continue kneading the dough for about 3-4 minutes.
After 3-4 minutes, add in your room temperature unsalted butter as well to the dough and continue mixing for an additional 9-10 minutes until the dough becomes nice and smooth.
To check when your dough is finished kneading, you can grab a small piece of the dough and try to stretch it out until it becomes somewhat translucent. If the dough does not tear when you doing this then it has been sufficient kneaded.
Now transfer the dough to a greased large bowl, shape the dough into a round ball, and then cover it with plastic wrap or a towel and let it proof in a warm place until double in size (about an hour).
After an hour has passed, de-gase the dough and transfer it to a lightly floured working surface.
Shape the dough into a round ball and then weigh the dough.
Now divide the dough into 10 pieces and weigh out each piece so that you get equal portion sizes.
Next, shape each dough into a round ball and then cover the dough with plastic wrap to prevent it from drying out.
Let the rough rest for about 10-15 minutes to relax the dough.
Afterwards, grab each piece of the dough and roll it out into a rectangular shape, slightly larger than the size of your slices of ham.
Now place a slice of ham on top of the dough and then roll the dough from one end into the other into a log shape starting from the wide end.
Now pinch the ends of the dough to seal it and roll it out using the palms of your hands to make it more smooth.
Then, bring the two ends of the dough together, pinch the two ends to seal them together.
Next, make a cut all the way to the end of the dough but just before the ends where you sealed it meet. You want to have a little bit of dough still together as we will need to fold it now. Leave about 2-3 inches uncut at the end.
Now, separate the two ends of the dough where you made a cut and lay the dough flat on the countertop.
Repeat these steps for all of the other pieces of dough.
Once finished, place all of the dough onto a baking tray lined with parchment paper and cover the dough with plastic wrap or a towel. Let the dough rise in a warm place for about 45-50 minutes.
In the meantime, you can prepare the egg wash and toppings for the bun.
For the egg wash, combine 1 beaten egg with a splash of milk and mix well.
For the topping, combine the cooked corn, mozzarella cheese, Kewpie mayo, and dried parsley together.
Once the buns have finished proofing, apply the egg wash to the buns then add in a generous amount of the topping to the top of the buns as well.
Finally bake the buns in a pre-heated oven at 350°F (180 °C) for about 18-20 minutes or until the buns are golden brown.