First start with the dough by adding the yeast to the warmed plant milk and leave for 5-10 minutes.
In a large bowl, add flour and tapioca starch and mix.
Add milk, maple syrup and rapeseed oil to the flour and mix briefly with a wooden spoon until a dough forms.
Transfer to a surface dusted with flour and knead for 10 minutes.
Place back in bowl and cover loosely with clingfilm and leave in a warm place for 1 ½ hours.
In the mean time, prepare custard by making a paste with the plant milk and cornstarch.
Pour into a saucepan along with turmeric, coconut milk, vanilla extract, melted vegan butter, maple syrup and agar agar.
Bring to a simmer, around 10 minutes, whilst stirring continuously to avoid any lumps then remove from the heat.
Fold in the mashed potato and make into a mushy dough then leave to chill in the freezer for 30 minutes (or fridge for 1.5 hours).
When the dough has proved, knead another 3 minutes then break into 20 pieces and shape into balls.
Roll each ball out using a rolling pin until around 7cm in diameter.
Place into palm of hand then add heaped tbsp of chilled custard into centre.
Gather the dough so that all ends meet at the top of the custard and pinch tightly to seal.
Place on baking tray lined with greaseproof paper, cover loosely with clingfilm and allow filled buns to rest for 30 minutes.
Place in steamer (ensure they do not come into contact with water), leaving a space of around 5cm between each bun.
Steam for 10 minutes then cool down for 2 minutes before serving.