Soft and fluffy steamed buns are filled with savory and sweet molten lava salted egg yolks custard filling that will gush out as soon as you take that first bite
If using salted egg yolks, steam the egg yolks for about 5 minutes over high heat and then mash with a fork or use a mini food processor to process into a fine paste
If using salted egg yolk powder, combine with 4 tsp of water into a thick paste consistency
Place the gelatin powder and water in a small bowl to let it bloom for 5 minutes
In a saucepan, add butter and let it melt over medium-low heat. Remove from the heat. Let it cool down to until lukewarm. Add sugar, milk powder, custard powder, and heavy cream. Whisk to combine. Add the mashed salted egg yolks or egg yolk powder paste (depending on which one you use) into the saucepan and whisk to combine.
The mixture will be grainy. Strain the mixture to get a smooth filling
Add the bloom gelatin to the strained egg yolk mixture.
Place the container in a pot of warm water (not boiling water) to melt the gelatin while stirring it
Transfer the egg yolk mixture to a shallow plate. Cover with a cling wrap and freeze the mixture in the freezer for about 1 hour. This will partially freeze it.
Scoop and portion into 8 portions (about 30 grams each) and lightly oiled your palms and roll each portion into a round ball. It will still be kinda sticky and that's normal. Place in a container lined with parchment paper. Let them continue freeze overnight in the freezer
Preparing the dough with a machine:
Place the flour (either option 1 or 2), instant yeast, salt, sugar, and cooking oil in a mixing bowl. If you are using a stand mixer, use a dough hook attachment. Gradually add liquid. If the dough still a bit dry, add a bit of water or milk. Add more teaspoon by teaspoon until the dough comes together and continue to knead for 10-12 minutes, until the dough is smooth and elastic. It feels slightly sticky to touch. It should clear the sides of the bowl but stick to the bottom of the bowl. Oil your hands a bit to help you pick up the dough and to prevent the stickyness
Prepare the dough by hands:
Place the flour (either option 1 or 2), instant yeast, sugar, and cooking oil in a mixing bowl. Mix everything until you get a rough dough (it's not going to be smooth yet). Cover and rest it for 15 minutes. Then go back and knead it. You'll be surprised by how easier it is to knead it now. Knead until the dough is smooth and pliable, about 15-20 minutes. Add liquid as needed. At any point during kneading, you can always stop and rest the dough if you find it hard to knead. This is to relax the gluten. Then go back to knead again and you'll be surprised by the difference it makes by just resting the dough before kneading again. It's easier for you too
Wrapping:
Place the dough on a lightly floured surface. Divide the dough into 8 equal pieces. Roll each dough into a round dough ball. Keep them covered.
Flatten the dough with your palm and use a small rolling pin to roll into a circle about 5 inches, slightly thicker on the center. Don't roll the dough out too thin too. This is important because the filling will make the dough "wet" if it's too thin and as a result, your steamed buns will have wrinkly surfaces (wet spots)
Place the frozen filling ball in the center of the wrapper
Gather all the sides to the middle and pinch to seal. Make sure it is sealed tightly to prevent any leaking.
Roll the dough in between your palm to get a smooth round
I place each shaped dough in a muffin paper liner, seam side down.
Then put it in an individual mini tart pan. This is optional. It helps to keep the dough round and tall. Because the filling softens when you proof the dough later, so the dough may widen to the side without any support. If you don't have such mini tart pan, don't worry about it. The buns will have wider and flatter appearance because of the filling
Proofing:
Let the dough rise at room temperature or at a warm place (but not too warm that the filling might melt). They won't necessarily double in size, but at least puff up to about 50% of the original size. This may take about 1 hour at a warm temperature. Don't go by the time however. The buns will feel lighter and when you push on them gently with your finger, they will spring back slowly. These buns are ready to be steamed
Steaming:
Bring the water in a steamer to a boil. Wrap the lid with a cloth. This will prevent water dripping from the lid and create burn spots
LOWER THE HEAT TO MEDIUM. Place the buns in there, leaving about 1-inch space in between. Cover with a lid but leaving it about 1/4-inch gap for some steam to escape. Steam on medium heat for 8 minutes
Once the buns are done steaming, turn off the heat and wait for 5 minutes before opening the lid so the buns will not collapse or wrinkle due to sudden change in temperature.
Serving:
They are best when served warm. Warn whoever that is eating this that the filling is HOT and it's thick and flowy, not extremely runny (because of the gelatin). So I find it easier to eat. The filling won't be flowy anymore once it has cooled down. It's just a very soft custard. Simply reheat briefly for that thick lava consistency
You can read more details on ingredients, substitutions, variations, and other tips in my post that may answer your questions not covered in the recipe card