Soak the dried shitake mushroom with clean water 2 hours ahead. Then slice thinly. Cut the garlic chives into 1-inch-long pieces and set it aside.
To make the aromatic water, add scallions, ginger, garlic, Sichuan peppercorns and water (or the mushroom soaking liquid) into a blender. Blend into a puree, then go through a sieve.
Take 2 tbsp of the aromatic water and mix with 1.5 tbsp of cornstarch; Reserve to marinade the pork
Mix the remaining aromatic water with 5 tbsp of cornstarch; Reserve to bind the filling later.
Cut 1 lb of pork loin into thin strips. Marinade it with salt, baking soda, Chinese cooking wine, some black pepper to taste, the cornstarch aromatic water and a drizzle of vegetable oil. Mix thoroughly. Set it aside for 15 minutes.
Preheat your wok until smoking-hot. Add cooking oil and the marinaded pork. Stir for few minutes or until most of the meat has changed color. Remove from the wok and set it aside
If the wok looks dry, you can add one more teaspoon of oil. Toss in the mushroom, bean sprout and stir over medium heat for a couple of minutes. Add soy sauce and oyster sauce. Introduce the pork back to the wok. Add the garlic chives and sesame oil. Pour in the cornstarch aromatic water to bind all the ingredients together. Mix thoroughly, and remove everything from the wok.
Mix 2 tbsp of all-purpose flour with 3 tbsp of water; we will use it as the glue to seal the egg rolls.
To wrap the egg rolls, put 2-3 tbsp of filling in the middle of the wrapper. Lift up one corner and fold that over. Pull it back tightly to compact the filling. Give a solid press of each side. Fold both sides to the middle. Apply some slurry at the last corner. Roll over the rest of the wrapper and seal it.
Heat your oil to 370 °F. Deep fry the egg roll for 5-6 minutes or until golden brown.
Serve the egg rolls with Worcestershire sauce.