Delicious and great fun, these buns are filled with a tasty take on chicken katsu.
Make the dough. Place the flour, sugar, salt, baking powder, yeast and oil in the bowl of a stand mixer fitted with the dough hook. Mix on slow speed to combine, then, with the mixer still running, gradually add the warm water, until you have a soft, smooth dough (you may not need all the water). Mix for 5 minutes on slow speed, then turn off the mixer.
Remove 50g of the dough, place it in a small bowl and cover it with cling film. Add the turmeric to the dough remaining in the mixer bowl and mix again until the dough is evenly coloured. Remove bowl from the mixer and cover it with cling film. Leave to rise in a warm place for 30¬–60 minutes, until doubled in size.
While the dough is rising, make the filling. Heat the oil in a small pan and add the onion, carrot and celery. Cook on a medium heat for about 4 minutes, until the onion starts to caramelize. Add the garlic and ginger and cook for about 1 minute, then add the curry powder and turmeric and cook for another 1 minute.
Pour in the coconut milk, soy sauce and agave syrup, cover the pan with a lid and simmer on a low heat for 15 minutes, until the vegetables have softened. Mix the corn flour with 1 teaspoon of water to form a paste, then stir this into the sauce. Bring the sauce to the boil, then stir continuously for about 2 minutes, until thickened. Pour the mixture into a food processor and pulse until smooth. Then, spread the sauce on a plate and leave to cool. (You will have too much to fill the buns – you can freeze any leftovers for another time.) Arrange the diced chicken into 8 little heaps.
Once the dough has double in size, tip it out onto a lightly dusted work surface. Using your hands roll it out into a log and divide it into 8 equal pieces, each about 50g. Roll each into a ball, dust with flour and place on a square of baking paper. Cover with oiled cling film and leave to rise for 10 minutes.
Take one dough portion and flatten it with your hand, pressing from edge to centre to form a disc about 10cm in diameter, with a slightly thicker centre than edge.
Place a generous teaspoonful of curry sauce into the middle of the dough disc and top with one portion of the chicken. Fold and stretch the dough to cover the filling completely, pinching the top together to seal. Shape into a neat ball and place the bun back on its square of baking paper. Repeat for all the other dough balls, then cover them with oiled cling film and set aside.
Cut the reserved 50g of dough into 4 equal pieces. Keep one piece white and colour another red, another orange and the final piece black, massaging the gels in with your hands so that each portion is an even colour.
On a lightly floured work surface, flatten out the white portion of dough. Using the end of the piping nozzle, if you wish, cut out 16 little white circles and attach them to the buns as eyes. Break off tiny pieces of the black dough, roll and fix them in the centre of the white circles as pupils. Roll out the red dough and, using scissors, snip it into little serrated strips to make 8 red chicken combs. Place these on top of each chicken head (you may find it easier to snip the shape once the red strips are in place). Add a little flour to the dough portions if they are a bit too stretchy to work with. Leave the buns to prove for 10 minutes.
Fill a pan one third full with water and bring to the boil. Depending on the size of your steamer basket, place 1 to 3 buns at a time inside, allowing room for them to double in size. (If you have a two-tiered bamboo steamer, you may be able to steam the buns in one go.) Place the steamer basket on the pan, cover with a tight-fitting lid and steam for 15 minutes, until cooked through. Repeat for the remaining buns.
Remove the buns from the steamer and leave them to cool slightly before serving them with any remaining sauce.