Heat 1–2 tablespoons of neutral oil in a large skillet or wok over medium heat. Sauté the minced garlic and onion for 2–3 minutes until fragrant and softened.

Add the ground pork and break it up with a spatula. Cook over medium-high heat for 5–7 minutes, stirring frequently, until the pork is no longer pink and has turned a light golden colour.

Stir in the oyster sauce, soy sauce, hoisin sauce, black pepper, sugar, and ¼ cup (60 ml) water. Reduce heat to low, cover partially, and let it simmer, stirring occasionally.

While the filling simmers, dissolve the cornstarch in ¼ cup (60 ml) of cold water and stir until smooth. Set aside.

Continue simmering for 30–45 minutes total, stirring every 10 minutes. If the sauce reduces too quickly and the pan looks dry, add 2–3 tablespoons of water at a time. The filling is ready when the pork is very tender and the sauce is dark, glossy, and reduced.

Give the cornstarch slurry a quick stir (it settles), then pour it into the filling while stirring constantly. Cook for 1–2 minutes until the sauce thickens and coats the pork. Remove from heat and let the filling cool completely before assembling — hot filling will kill the yeast in the dough.

In a large mixing bowl, whisk together 2 cups (250 g) of the flour, the instant dry yeast, salt, and sugar until evenly combined.

In a small saucepan, combine the milk, water, and margarine or butter. Heat over low heat until the butter melts and the liquid reaches approximately 110°F / 43°C (warm to the touch but not hot). Do not let it boil — temperatures above 130°F / 54°C will kill the yeast.

Make a well in the flour mixture. Add the beaten egg and the warm liquid mixture. Stir with a wooden spoon until a shaggy dough forms. Gradually add the remaining 2 cups (250 g) of flour, mixing until the dough pulls away from the sides of the bowl. Turn out onto a lightly floured surface and knead for 8–10 minutes until the dough is smooth, soft, and elastic. Shape into a ball, place in a lightly oiled bowl, cover with a damp tea towel or plastic wrap, and let rise in a warm spot for 30 minutes until roughly doubled in size.

Punch down the risen dough and turn it out onto a lightly floured surface. Knead briefly for 1–2 minutes. Divide the dough into 8 equal pieces (use a kitchen scale for evenness — each piece should be about 95–100 g). Roll or press each piece into a circle roughly 4–5 inches (10–12 cm) in diameter, keeping the centre slightly thicker than the edges.

Place 2–3 heaping tablespoons of cooled filling in the centre of each dough circle. Gather the edges up and around the filling, pleating as you go, then pinch and twist the top firmly to seal. Place each bun seam-side down on a small square of parchment paper.

Arrange the sealed buns in your steamer basket, leaving at least 2 inches (5 cm) between each bun to allow for expansion. You will likely need to steam in 2–3 batches depending on your steamer size.

Bring about 1 litre of water to a rolling boil in the pot beneath your steamer. Place the steamer basket over the boiling water, cover tightly, and steam for 15 minutes over medium-high heat. Do not open the lid during steaming. When done, turn off the heat and let the buns sit in the covered steamer for 2 minutes before removing — this prevents the buns from collapsing due to sudden temperature change.