Finely dice the ham. Finely chop the scallions and place them in a small bowl. Add the tiny pinch of baking soda and mix well with your fingers. This will help the scallions stay bright green after steaming. Set both aside.

In a very large mixing bowl, whisk together the eggs, milk, instant yeast, and sugar until well combined and the yeast is dispersed.

Add the all-purpose flour to the wet ingredients. Use a sturdy spatula or chopsticks to mix until a shaggy dough forms and no dry flour remains.

Pour the corn oil over the dough. Use your hands to roughly incorporate the oil into the dough in the bowl until it's mostly absorbed.

Turn the dough out onto a clean, un-floured work surface. It will be sticky at first.

Knead using a "laundry scrubbing" motion: press the heel of your hand into the dough, pushing it away from you, then fold it back over itself. Give it a quarter turn and repeat. Continue for 10-15 minutes. The dough is ready when it transforms from sticky to smooth, soft, and elastic. It will lose its stickiness and feel supple. You do not need to achieve a windowpane.

Once smooth, stretch the dough out slightly on your counter.

Scatter the diced ham and the baking soda-coated scallions evenly over the surface.

Fold the dough over the toppings and begin kneading again for just 2-3 minutes, until the ham and scallions are evenly distributed throughout the dough.

There is no first proof.Take the dough directly and roll it out on a lightly floured surface into a large rectangle, roughly 40cm x 30cm (16" x 12") and about 0.5cm (1/4") thick.

Sprinkle an even, generous layer of pork floss over the entire surface, leaving a 1cm border at the top edge.

Sprinkle a thick, even layer of shredded cheese over the pork floss.

Starting from the bottom long edge, tightly roll the dough up into a log, like a cinnamon roll.

Pinch the seam firmly to seal.

Using a sharp serrated knife or bench scraper, cut the log into 12 equal pieces, each about 4-5cm (1.5-2") wide.

Spread a thin layer of salad dressing on the two cut sides of each roll.

Press each cut side into a bowl of additional pork floss to coat completely.

Arrange the rolls in your steamer basket(s), leaving plenty of space between them as they will expand. Cover the steamer with a lid or plastic wrap.

Let the rolls proof in a warm, draft-free place (e.g., a turned-off oven with the light on) until they have doubled in sizeand feel very light and puffy to the touch. This should take 30-45 minutes depending on warmth.

Once proofed, lightly brush the top of each roll with a little water and sprinkle with black sesame seeds (if using).

Bring the water in your steamer to a full, rolling boil over high heat. Carefully place the steamer basket(s) over the boiling water.

Steam on high heatfor 15 minutes. It is crucial to start timing only once the steam is actively rushing out from under the lid.

After 15 minutes, turn off the heat. DO NOT OPEN THE LID.Let the rolls sit in the steamer, covered, for 5 full minutes. This resting period prevents them from collapsing due to sudden temperature change.

After 5 minutes, remove the lid. Lift out the rolls and serve immediately while warm and soft, with the cheese perfectly melted.