Prepare salted egg yolk custard: (can be prepared the day before)
Combine custard powder, egg, sugar, condensed milk, cake flour, and milk in a saucepan. Use a whisk to stir until combined and no lumps. Put this on the stove over medium-low heat and keep whisking until the mixture starts to thicken. It can coat the back of a spoon or spatula. Add the butter and continue to stir until the butter has melted. Add the mashed salted egg yolks and desiccated coconut. Whisk to combine. The mixture is lumpy because of the salted egg yolk crumbs and the coconut. Cover with a cling wrap, touching the custard directly and set aside to let it cool down completely before using
Prepare the dough:
Place both of the flour, instant yeast, sugar, salt, in a mixing bowl and stir to combine. Add milk and oil in a mixing bowl. Give the mixture a stir
Turn on the mixer at the lowest speed to prevent flour from flying all over the place. Continue to knead at low speed (speed 2 on KA) until the dough is smooth and elastic
Cover and let the dough rest for 15 minutes to relax the gluten so it is easier to shape
Shape the dough:
Lightly dust your work surface with a bit of flour if necessary. Use a rolling pin to roll the dough out into about 10 x 15 inches (25.5 x 38 cm) rectangle. Don't have to be exact. Use a bench scraper to cut halfway in the middle of dough
Spread the filling (reserving about 2-3 Tbsp for later) as shown in the photo, leaving one area empty
Fold that area over the top
Then fold to the side
And lastly the last fold
Use a rolling pin to gently flatten the dough slightly to even out
I cut the dough into half in the middle. This is also so that it can fit in my steamer and I can have more layers
Spread the rest of the filling you saved earlier on top of one of the dough
Stack the dough on top of the other
Proof the dough:
Place the dough on top of a large piece of parchment paper. Transfer to a steamer or a steaming basket, but do not turn on the steamer yet. We are not steaming yet. Let the dough proof at a warm place until it is puffy.
It may not double in size, probably only about 50% puffy. The dough should feel light and when you gently use your finger to push on the dough, it should bounce back very slowly and leave a bit of indentation. The dough is done proofing. Mist the surface with a bit of water and then sprinkle with some white sesame seeds. This is optional. You can skip if you don't want to
Steaming:
If you use a bamboo steamer, you don't need to wrap the lid with a cloth. If not, wrap the lid with a cloth to prevent water condensation from dripping on the surface of the dough, creating burn spots
Fill up the steamer (or large pot) with some water. Place the steaming basket on top. Turn on the stove and bring the water to simmer over medium-high heat. When the water has come to a simmer, lower the heat to medium. Crack the lid open a bit to let some steam out. This prevents the steamed buns from wrinkle. Steam for 30 minutes or until the buns are cooked through. The buns will spring back when you touch it
Turn off the heat and don't open the lid yet. Let it sit for 5 minutes. This helps to prevent the buns from collapsing due to sudden change in temperature
Remove the steaming basket from the steamer and let it cool down slightly before serving
To serve:
I trim off the edges for a neater look.
Cut into smaller squares or rectangles suitable for serving size