A traditional artisan bake offering a delicate, buttery crumb and golden exterior, served fresh with clotted cream, preserves, or rich salted butter.
Dissolve the yeast and sugar in warm water, add the flour and oil, and knead into a soft dough.
Cover and let the dough rise until doubled, about 1 hour.
Mix the mashed egg yolks, butter, icing sugar, and milk into a smooth paste, then chill until firm.
Divide the dough, roll each piece into a wrapper, and seal a spoonful of custard inside.
Rest the buns for 30 minutes.
Steam over medium-high heat for 10 minutes until puffed and glossy.
Serve warm so the custard stays molten.