Heat the almond milk until it is lukewarm. Add in the sugar and yeast. Give the mixture a stir and leave it to become foamy.
Add the flour, hojicha, avocado oil and vanilla extract to a stand mixer bowl fitted with a dough hook.
Pour in the yeast mixture and knead until the dough becomes smooth and elastic.
This is a small amount of dough, so if your stand mixer bowl is a larger capacity, you may want to do this by hand. (Simply add all the ingredients into a bowl and knead by hand).
Lightly grease a small bowl and transfer the dough to it. Cover with a damp cloth. Leave it to rise in a warm location, until almost doubled in size.
When the dough has risen, deflate the dough and divide into 6 equal portions.
Roll out the dough into a disc and place the chestnut filling in the centre. Gather the dough around the filling and pinch the seams to enclose.
To attain the flower petal shape, flatten the filled bun into a disc with a rolling pin, about 2cm in thickness. Don't flatten it too thinly or the filling will burst out.
Make a small round mark (about 1cm in diameter) in the centre of the flattened bun. (You can use a wide straw to make a light indentation).
Next, use a sharp paring knife and make 5 slits of equal distance around the circumference of the disc. You'll end up with 5 segments.
Then pinch the tips of each segment together to form the petals.
Repeat with the remaining dough.
Cover the buns loosely with plastic wrap or a damp cloth and let them rise in a warm location until just slightly puffy. [It's better to bake the buns slightly underproofed to retain their shape].
Preheat the oven to 350°F/177°C.
Brush the centre of each flower bun with some milk and sprinkle on some black sesame seeds (for decoration).
Bake the buns at 350°F/177°C for 13-15 minutes.
Remove from the oven and let cool on a wire rack. Store buns in an airtight container at room temperature for up to 3 days.