(Option 1) Using a mixer: Add flour and turn on at low speed. Gradually add water. Let mix until the surface of the dough becomes smooth, about 8 minutes.
(Option 2) Kneading the dough by hand: Add flour to a large bowl. Gradually add water and whisk flour with a spatula until water is fully blended. Dust both hands with dry flour and knead the dough. If there is dry flour in the bowl that is difficult to blend into the dough, add a bit more water to the dry flour, 1 tablespoon at a time. Knead until there is no dry flour left. The dough should feel springy and you should be able to easily pick it up without it sticking to the bottom of the bowl. Dust a working surface with dry flour and transfer the dough onto it. Knead until the surface of the dough turns smooth.
Wrap and seal the dough with plastic wrap. Let for 30 minutes up to 3 hours.
To make the filling
Prepare the filling while resting the dough. Combine ground beef, minced ginger, Shaoxing wine, light soy sauce, dark soy sauce, and ground Sichuan peppercorn (or black pepper) in a big bowl. Mix well until the liquid ingredients are fully absorbed.
Prepare and cut vegetables, but do not add them to the ground beef yet.
Right before assembling the pies, add the onion, carrot, salt and sugar to the beef filling. Mix well. Add sesame oil and mix again. (*footnote 1)
To assemble the pies
Add oil to a small bowl and prepare a small brush. Dust both hands and a large cutting board with dry flour. Transfer the dough to the cutting board and knead for a few times. The dough should be a bit softer, springy, and smooth.
Divide the dough into two equal pieces and put one piece back in the bowl and cover it with plastic wrap. Roll the other half into a ball. Press it into a flat circle. Use a rolling pin to roll it into a thin round disc, about 4 millimeters (1/8 inch) thick.
Brush a thin layer of oil on top. Sprinkle a pinch of salt over it and brush it again until evenly spread. Roll the round sheet into a long stick. Cut the stick into 6 equal pieces.
Work on the meat pies one at a time. Cover the rest of the dough with plastic wrap.
Pinch the two ends of each piece to seal the oil inside. Press the dough (the sealed ends are on the left and right) and gently roll it into a thin round disc. This step is help to create a layered crust.
Scoop 2 to 3 tablespoons of beef filling and place it on one side of the dough pancake, in a half-moon shape, as if making a quesadilla.
Fold the empty half over and press the edges together by hand. Turn the edge upward and press it again to further seal the pie.
Set pie aside and work on the rest of the dough in the same manner.
Cover the meat pies with plastic wrap while working on the rest of the pies, to prevent the dough from drying out.
To cook the pies
Heat a large nonstick skillet with 1 tablespoon oil over medium heat until warm. Transfer meat pies to the skillet without overlapping. Brush the top side with oil. Cover skillet and cook over low heat until the bottom side turns golden brown, 3 to 4 minutes. Flip with a spatula and cook the other side. Cover and cook until the bottom side turns golden brown, 3 minute. Transfer the meat pies to a plate. Cook the remainder of the meat pies the same way.
Serve warm with Chinese black vinegar. If the meat pie is not salty enough, blend 1 teaspoon light soy sauce with 1 tablespoon black vinegar as a dipping sauce.
To store the meat pie
Place meat pie in an airtight container. Store in the fridge up to 3 days or in the freezer for 1 month.
To reheat the meat pie. Heat oil in a skillet until warm. Add meat pies. When the skillet is hot, add 2 to 3 tablespoons water and cover immediately. Flip once during the cooking. Cook until both sides are crispy and the inside is hot.
Do not mix the filling too soon before the dough is ready. It will make the filling watery later.