- Start by making the dough.
 Combine dry ingredients in a 
bowl, then add water little by 
little and bring dough together
 using your hands; you should
 have a sticky ball. Turn out onto 
a floured surface and knead 
5 minutes, until smooth and
 bouncy, then place in an oiled 
bowl. Cover with a kitchen towel
 and leave in a warm place to 
double in size for 1 to 1½ hours. 
- Meanwhile, put vinegar for
 pickled cucumber into a small
 saucepan with 3 Tbsp water.
 Bring to a simmer, then pour
 into a bowl, add cucumber, and
 leave to cool. 
- Turn dough onto a floured 
surface, knead for 1 minute to
knock out air, then divide into
 10 equal pieces. Take one piece, 
flatten into a ½-inch-thick disc,
then brush one half with a little 
oil. Fold bun into a half-moon 
and place on a small square of
parchment
 paper on
 a tray. Repeat with
 remaining dough, then
loosely cover tray with a 
kitchen towel and leave to 
rise for 30 minutes more. 
- For filling, in a small bowl,
whisk soy sauce, peanut butter, 
vinegar, garlic and sesame oil.
 Heat canola oil in a frying pan on 
high, then fry mushrooms 6 minutes,
until soft and browning at 
the edges. Stir in sauce to coat,
then turn heat to medium and
 cook, stirring regularly, 5 minutes,
 until sauce reduces and darkens. 
- To cook the bao, set a
steamer over a pan of simmering
 water. Put the bao, still on
 their parchment-paper mats,
 into the steamer in batches,
 making sure they don’t touch. 
Cover and steam 8 minutes. 
- Once done, fill each bao 
with a generous tablespoon
 of mushrooms, 3 or 4 slices
 of cucumber and, for a little 
crunch, some peanuts.