Combine flour, sugar, yeast, baking powder and salt in a mixing bowl.
Incorporate the warm water into the dry ingredients slowly until the dough is sticky. Stir in 1 tbsp of vegetable oil.
This is what the dough should look like after the water has been mixed in.
If using an electric mixer, use the dough attachment, start on a low speed then increase as the dough forms and is kneaded by the mixer, see video. 15 min total kneading time.
If kneading by hand, spread a small handful of flour on a board. Knead until the dough is smooth with no lumps and is no longer sticky, approx 10 min.
Cut dough into three equal parts.
Set aside two pieces under a damp paper towel. Take one piece, knead it a few times and form into a round ball. Begin to roll it with a rolling pin into a large flat pancake until about 1/4 in thick.
Spread a thin layer of oil on the pancake, spread it evenly using your fingers. Spread a thin layer of salt as well.
On top of the oil and salt layer also spread a small handfull of chopped scallions.
Starting at the edge, begin to tightly roll the pancake into a long roll. Roll as tightly as possible. Pinch the finished edges.
Using the palm of your hand, flatten the roll while gently stretching it out, removing all air bubbles. Roll again into a bun, tuck the end underneath the bun, set aside.
Repeat steps 7-11 with the remaining dough.
Roll the bun into an approximately 12 in wide, 1/2 in thick pie.
Lightly brush the surface of the pie with water.
Sprinkle sesame seeds generously onto the wet surface of the pancake. Use the rolling pin to gently press the seeds into the pancake.
Using low heat, pre-heat a flat heavy bottomed pan, cast iron is ok. Vegetable oil is not needed for this step. Once the pan is hot, gently place the pancake sesame side down. Cover the pan.
Cook covered for 5-6 min until a golden brown crust forms. Flip and cook the other side covered approx 3-4 min, until golden brown as well.
Cut into wedges and serve with roast duck, or any meat dish. It stores very well in the fridge for about a week, use an airtight container. This recipe makes 3 pies.