In a large mixing bowl, mix the flours. Stir the water in slowly and then add vegetable oil. Knead the dough for several minutes until all the ingredients are well combined.
Brush some oil on your container and then transfer the mixture in. Press the surface and then steam for around 30 minutes (depending on the thickness). And then cool down slightly.
Place a plastic wrapper on a clean surface and then transfer the steamed mixture out. Fold the plastic wrapper back so the upper side of the mixture is covered with plastic wrapper, otherwise, it might be quite sticky. Knead the dough for several minutes until smooth or pat with a rolling pin.
Divide the dough in half and then shape on half into a round 3 cm diameter log and the other half into several 1 cm diameter long log. Cover each one with plastic wrappers and put into fridge overnight to finalize.
Cut the 1cm diameter long log into 5~7 cm long sections and slice the 3cm diameter long log.
Divide the dough into four portions and then shape each one to a long log.
Brush some oil on your steamer and then place them one by one.
Steam for around 30 minutes until cooked. Transfer out and cool down.
Cut into slices before using.