Chinese Meat Pie

Name: Chinese Meat Pie
Prep time: 20 min
Cook time: 10 min
Total time: 30 min
Cuisine: Chinese
Ingredients: 300 g beef ( , with 15% to 20% fat); 2 large scallion ( , finely chopped); 1/2 tsp. Sichuan peppercorn powder; 1/2 tsp. salt; 2 green onions; 1 thumb ginger ( , sliced ); 1 tbsp. light soy sauce; Pinch of fresh ground pepper; 1 egg; 1 tbsp. oyster sauce; 1 tbsp. sesame oil; 1/2 tsp. sugar; 1 tbsp. Shaoxing cooking wine; 1/2 middle size white onion; 2 cups all-purpose flour; 1/2 cup hot water over 90℃; 60 ml room temperature water ( , plus 10ml more for adjusting); 1 tbsp. vegetable cooking oil; pinch of salt