In a small sauce pan, prepare your Tangzhong by adding in your bread flour and water. Heat the pan on low heat while constantly stirring it until the flour water mixture turns into a thick paste.
Remove the Tangzhong from the stove and cover it with plastic wrap and store it in the fridge for at least 20 minutes to allow the Tangzhong to cool down.
Next, in a large mixing bowl, add in your bread flour, sugar, salt, instant yeast, milk powder, egg, the Tangzhong that you made earlier, and the milk.
Mix & knead everything well together until you don't see any more white flour bits on the dough. This should take you about 2-3 minutes.
Then cover the bowl with plastic wrap or a towel and let it rest for 20 minutes at room temperature.
In the meantime, prepare your pineapple topping by creaming together the white sugar and butter.
Then add in your vanilla extract and 1 egg yolk and everything together.
In another bowl, combine your cake flour, table salt, baking powder, baking soda and milk powder together.
Now sift your dry ingredients over your wet ingredients using a sieve and then mix everything well together.
Then transfer your pineapple topping to plastic wrap and shape it into a long rectangle log.
Once done, cover it with the plastic wrap and store it in the fridge for later use.
After 20 minutes have passed, you can start working on your dough from earlier. Transfer the dough over to your countertop and then flatten it with your hands.
Tip: Add some oil to your hands to help prevent the dough from sticking to your hands.
Then add 20g of unsalted butter to the dough.
Fold the dough over the butter and then knead it for 2-3 minutes to incorporate the butter into the dough.
After 2-3 minutes of kneading the dough, we are going to use the slap and fold method of kneading our sticky dough.
Grab the sides of the dough, lift it up into the air and then slap it down onto your countertop and fold the dough over itself.
Then grab the sides of the dough with your hands perpendicular to the dough, lift it up, slap it down and fold it over the dough.
Repeat this process of slapping and folding the dough until it becomes nice and smooth and less sticky to handle.
This process will usually take at least 10-15 minutes to do.
Then spend another 2-3 minutes kneading the dough once it becomes less sticky.
Once the dough becomes very smooth and easy to handle, shape it into a round ball.
Place the dough into a large greased bowl.
Cover it with plastic wrap or a towel and let it proof in a warm place until double in size (about an hour).
After the dough is done proofing, de-gase the dough by punching down on it and then transfer it to a floured countertop.
Shape the dough into a round ball and then weigh the dough.
Now divide it into 10 pieces and then weigh out each piece to get equal portion sizes.
Then shape each piece into a round ball by folding the sides of the dough inwards with one hand while rotating the dough with your other hand.
Pinch the bottom of the dough to seal it then roll it in a circular motion on your countertop using the palm of your hands to make it into an even round ball.
Next place all of the pieces of dough onto a baking tray lined with parchment paper and cover it with plastic wrap or a towel and let it proof in a warm place for about 45-50 minutes.
When the dough is done proofing, prepare your pineapple topping to go on top of the buns. Take the pineapple topping that we prepared earlier from the fridge out and then weigh out the pineapple topping.
Next cut it into 10 pieces and then weigh each piece.
Then shape each piece into a round ball by rolling it with your hands.
Now taking a piece of plastic wrap, place 1 piece of the pineapple topping in the middle. Then grab one end of the plastic wrap and cover the pineapple topping.
Next using the palms of your hands or a dough roller, flatten out the pineapple topping until it is slightly wider than the dough. We will be placing this on top of the dough so it should be wider than the dough.
Once you've finished flattening out the pineapple topping, remove the top piece of plastic wrap covering the pineapple topping.
Now holding the bottom of the plastic wrap with the pineapple topping exposed on top, place the pineapple topping on top of one of the pieces of dough that we made either.
Repeat this process for all of the other pieces. After your done, prepare an egg wash to apply to the top of the buns by mixing together 1 egg + a splash of milk.
Once you're finished applying the egg wash to each bun, bake the buns in a preheated oven at 350°F (180°C) for about 14-15 minutes or until the top is golden brown.