Stir the vegetable oil and cold water into the tangzhong then let the mixture to cool to lukewarm.
25 g vegetable oil, 40 g cold water
Mix in the egg and egg yolk, vanilla, orange zest and lemon zest until smooth.
1 egg, 1 egg yolk, 1 tsp vanilla bean paste, 1/2 orange, zest finely grated, 1/2 lemon, zest finely grated
Add the yeast, both types of flour and potato starch (or cornflour) to the bowl. Add the sugar and salt on top then stir to get a rough dough.
2 tsp instant yeast, 120 g flour (I used a mix of plain white & wholemeal spelt flour here), 40 g potato starch or cornflour, 1 tbsp granulated sugar or caster sugar, 1/2 tsp fine table salt
Tip the dough out onto a lightly floured surface and knead, dusting with a little more flour as needed to prevent sticking. Knead for 5-10 minutes until the dough is smooth and less sticky.
Place the dough back into the bowl and drizzle on some oil, turning the dough to coat. Cover the bowl with a damp tea towel (or reusable shower cap) and leave somewhere warm to rise until doubled in volume - 1-2 hours.