Why are these called ‘polo’ buns, you ask? Well, it’s a corruption of the Cantonese bo lo, which means pineapple – their mottled golden glaze crackles in the oven, making them look a little like a pineapple.
First, make the biscuit dough. In a large bowl, cream the butter until pale and creamy, about 3 minutes. Add the remaining ingredients and mix well: it may seem dry at first, but will soon form a stiff dough. Shape into a log, cover with plastic wrap and refrigerate until firm, about 1 hour.
Next, the bun dough. Put the lukewarm water, coconut milk, aquafaba and sugar in a large bowl. Whisk to combine, then sprinkle in the yeast and whisk again. Set aside until frothy, about 10 minutes. Stir in the oil, then gradually sift in the flour and salt. Mix with a wooden spoon until it starts to come together, then turn out onto a clean countertop and knead to a smooth, elastic dough, about 7 minutes. Return it to the bowl and cover with a damp tea towel. Set aside in a warm place until doubled in size, about 1 hour.
Now for the ‘char siew’ filling. Heat the oil in a large non-stick frying pan over medium-high heat and fry the onion until translucent, about 3 minutes. Add the soy sauce, sugar, sesame oil and hoisin sauce. Stir in the soy chunks and fry for another 2–3 minutes, then add the white pepper. Whisk the flour with
Punch the risen bun dough with your fist to knock it back, then turn out onto a well-floured countertop and divide into 10 pieces. Use a rolling pin to roll each one into a circle about 13–15 cm across, then place a heaped tablespoon of filling in the middle. Pinch the dough together at the top, completely enclosing the filling. When all the buns are rolled and filled, remove the biscuit dough from the fridge and divide into ten. Take a biscuit dough ball and cover with plastic wrap, then roll out into a circle about 5 mm thick and wide enough to cover the top of a bun. Place on the bun and score in a criss-cross ‘pineapple’ pattern.
Once all the buns are topped with biscuit dough, transfer to a baking tray lined with baking paper. Make the glaze by whisking the plant milk and agave syrup together. Brush over the tops of the buns, cover with plastic wrap and leave in a warm place to rise for 20 minutes.
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