Rehydrate the Mushrooms: Place the dried shiitake mushrooms in the hot water for about 2 hours, or until completely softened. Press out any extra water and remove tough stems. Chop the mushrooms very finely; you should have roughly ¼ cup.
Prep the Shrimp: Add shrimp to a mixing bowl with 1 teaspoon sugar, baking soda, and the water. Let it sit for 15 minutes. Rinse under running water until clear, then drain thoroughly.
Make the Pork Base: In a stand mixer (or by hand), combine the ground pork with the remaining 1 tablespoon sugar, cornstarch, Shaoxing wine, salt, and white pepper. Mix on medium-low for around 5 minutes until the mixture becomes tacky and cohesive. If mixing manually, stir in one direction for about 10–15 minutes until a sticky paste forms.
Combine Shrimp and Pork: Add the prepared shrimp to the pork mixture. Beat on low speed for 2 minutes, then raise to medium for 2 more minutes until well incorporated. (If mixing by hand, chop shrimp first and stir into pork mixture in one direction for 10 minutes.)
Add Flavor and Texture: Stir in the chopped mushrooms, neutral oil, oyster sauce, and sesame oil. Mix for an additional minute on medium speed (or by hand for 2–3 minutes).
Form the Siu Mai: Line your steamer with perforated parchment, cheesecloth, or napa cabbage leaves. Place a dumpling wrapper on your palm and add about 1 tablespoon of filling in the center. Gather the edges and mold into an open-topped dumpling. Smooth the top flat, and add a bit of finely minced carrot in the center for color.
Steam the Dumplings: Pour enough water into a wok or pot to reach halfway up the steamer base. Bring water to a simmer. Arrange siu mai 1 inch apart in the steamer and cover. Steam over medium heat for 9 minutes. Serve immediately with chili oil.
Make-Ahead Option: To freeze, place the assembled dumplings ½ inch apart on a parchment-lined baking sheet. Cover tightly with plastic wrap or a clean grocery bag and freeze overnight. Once frozen, transfer to an airtight container. Steam from frozen without thawing for 11 minutes.