Mix together the ingredients for the sauce and set aside
Add the pork, shiitake mushrooms, ginger, water chestnuts, scallions, egg, soy sauce, sesame oil, sugar, salt, and pepper to a bowl and mix
Combine the 2 Tbsp cornstarch with ¼ cup water and stir until cornstarch dissolves; pour into the meat mixture and mix
Fill a small bowl with water; orient the wonton skin in your palm in a diamond shape, and place ~1 tsp of the meat mixture in the bottom corner of the skin; roll the corner up and over the meat mixture about half way and then wet the skin to the right of the meat; holding the skin on both sides of the meat between your thumbs and pointer fingers (fingers facing towards you), pinch your fingers together and tuck the damp skin on the left onto the right to seal shut (the water will act as an adhesive)
Bring a large pot of water to a boil
Place wontons in boiling water in batches (you can usually cook 10-15 at a time depending on the size of pot) and cook until they begin to float; check with a meat thermometer to ensure internal temp is 165F or higher, then remove the wontons from the water with a mesh strainer (shake off excess water before adding them to a bowl)
Spoon some of the sauce on the wontons (leave some on the side) and top with some more scallions and sesame seeds - enjoy!