In a small sauce pan, add in your bread flour and water. Heat the pan on low heat while constantly stirring it until the mixture turns into a thick gelatinous paste.
Then remove the pan from the stove and transfer it to a small bowl or dish. Cover it with plastic wrap and then store in the fridge and let it cool down for at least 30 minutes before using.
You can also make your Tangzhong the night before as well.
To make the dough, in a stand mixer mixing bowl, we’re going to add in our bread flour, white granulated sugar, table salt, instant yeast, milk powder, an egg at room temperature + our Tangzhong from earlier.
Put the mixing bowl onto the stand mixer and give it a quick few whisks then slowly add in your room temperature milk to the dough.
Now continue kneading the dough for 3-4 minutes then add in your room temperature butter.
Continue mixing it for an additional 9-10 minutes.
To check and see whether or not your dough has been sufficiently kneaded, grab a small piece of the dough and stretch it out with your fingers until it becomes somewhat translucent and you can see light passing through it. If you do not see any rips or tears or very little, then your dough has been sufficiently kneaded.
Now transfer the dough to a greased large bowl.
Now apply a little bit of oil to your hands and then shape the dough into a round ball.
Place it back into the bowl and cover it with plastic wrap or a towel and let it proof in a warm place until double in size, approximately 1 hour.
In another bowl, add in your room temperature butter, white granulated sugar, and table salt.
Mix everything well together then add in your egg and continue mixing it until the egg has been incorporated into the mixture.
Then in another bowl, add in your pastry flour, milk powder, and custard powder and put everything through a strainer before adding it to your wet ingredients.
Continue mixing everything together until you no longer see any white flour spots.
Finally add in your desiccated coconut and mix everything well together.
Transfer the filling onto plastic wrap and shape it into a rectangle if possible. Then store it in the freezer for 30 minutes and then leave it in the fridge afterwards.
Now prepare the Mexican topping for the buns. In a bowl, add in your room temperature butter, white granulated sugar, and pastry flour.
Mix everything well together but don’t overmix it.
Put the topping inside of a piping bag with a small round tip and set it aside.
Once our dough has finished proofing, de-gase the dough and transfer it to a floured countertop.
Shape the dough into a round ball and then weigh it out on a scale.
Now divide it into 10 pieces and weigh out each piece so that you get equal portions.
Next, shape each piece into a round ball. Once done, cover the dough with plastic wrap or a towel and let it rest for 15 minutes to relax the dough.
During this time, take out the filling, weigh it out and then divide it into 10 pieces.
Shape each piece into a roll and then put it back into the fridge until you are ready to add the filling into the buns. This is to prevent the filling from melting too quickly.
After 15 minutes, take 1 piece of the dough, flatten it and then roll it out into an oval shape.
Take 1 piece of the filling that you made earlier and place it in the middle of the dough.
Now grabbing the sides of the dough, bring it together and then pinch the edges to seal the dough.
Give the dough a few rolls to make it into a circular oval shape and then place the dough onto a baking tray lined with parchment paper. Cover it with plastic wrap or a towel to prevent it from drying out.
Repeat the process for all of the other pieces. Now place the baking tray in a warm environment and let the buns proof for about 35-40 minutes.
Also preheat your oven to 350°F (180C°) while our buns are proofing.
During this time, place the Mexican topping that you made earlier into the fridge and let it sit there. This is to prevent the topping from melting too quickly in the oven when we’re baking our buns.
Once our buns are done proofing, take the topping out of the fridge and set it aside.
Now apply an egg wash to the top of the buns by combining 1 egg with a splash of milk and whisking it together.
Finally pipe the Mexican topping horizontally across the bun on both ends of the bun but don’t pipe it all the way to the edge otherwise the topping will melt and run all the way to the bottom of the bun when baking.
Sprinkle some sesame seeds on top of the buns and then bake them at 350°F or (180°C) for about 15-16 minutes or until golden brown at the top.