Cantonese Char Siu Bao — Steamed vs Baked Science

Ingredients

• For the char siu filling (both versions)
• 300 g char siu (roast pork), finely diced
• 2 tbsp oyster sauce
• 1 tbsp light soy sauce
• 1 tbsp sugar, slightly increased for the baked version
• For the steamed bao dough (zheng)
• 300 g plain flour, sifted
• 7 g instant yeast
• 150 ml whole milk, lukewarm
• 30 g caster sugar
• 1 tbsp neutral oil
• For the baked bao dough (ying)
• 300 g plain flour, sifted
• 1½ tsp baking powder
• ¼ tsp baking soda
• 2 eggs, 1 for the dough; 1 beaten, reserved for egg wash
• 30 g caster sugar
• 80 ml whole milk
• 30 g unsalted butter, softened

Method

1. 1
   Prepare the filling for both versions. Combine the finely diced char siu with oyster sauce, soy sauce, and sugar — using the slightly higher sugar measure if the filling is destined for baked bao, where the oven's caramelisation of the exterior can compete with a less sweet centre. Mix until uniform and set aside. The filling is ready when it holds together in a cohesive mass rather than sitting loose.
2. 2
   Make the steamed bao dough. Dissolve the yeast and sugar in the lukewarm milk and allow it to activate. Combine with the flour and oil and knead to a smooth, slightly tacky dough. Prove in a covered bowl until doubled in size. The dough is ready when a finger pressed into its surface leaves an indent that springs back slowly — not snapping back immediately (under-proved) and not collapsing (over-proved).
3. 3
   Make the baked bao dough. Sift the flour with the baking powder and baking soda — the ratio of these two leaveners determines the oven spring of the finished bao. Work in the sugar, one egg, milk, and softened butter until a smooth dough forms. Because this dough is chemically leavened, no proofing wait is required; proceed directly to shaping. The dough is ready when it is smooth and pliable and pulls cleanly from the work surface.
4. 4
   Divide and fill. Portion each dough into six equal pieces, approximately 60–65 g each. Flatten each piece into a round, place a spoonful of filling at the centre, gather the edges, and pleat closed. For the baked bao, score the sealed top with three or four shallow cuts to create the characteristic petal-split once baked. For the steamed bao, leave the sealed top unmarked — its split will be structural, not decorative.
5. 5
   Steam the steamed bao. This is where the dish lives or dies. Do not preheat the steamer. Place the proved bao — on squares of parchment — into a cold steamer, seal the lid, and bring immediately to maximum heat. The sudden, violent surge of steam forces the characteristic xiao kou (laughing) split at the crown. A preheated steamer delivers heat too gradually; the bao rise without splitting. Steam on maximum heat for 12–15 minutes. The bao are done when they have expanded visibly, the surface is dry and matt to the eye, and the dough yields but springs back firmly when pressed.
6. 6
   Bake the baked bao. Place the shaped and scored bao on a lined tray. Apply the first coat of beaten egg wash before loading the oven. Bake until the surface begins to colour, then apply a second coat of egg wash midway through baking. Two applications are required — a single wash produces insufficient colour depth. The bao are done when the exterior is deep golden and the scored petals have opened and set.
7. 7
   Rest the baked bao for five minutes after removing from the oven. The steam trapped inside redistributes during this period and softens the crust from within. The bao is ready to serve when the crust yields slightly under gentle pressure rather than crackling hard.