In a bowl, combine the shrimp and baking soda to coat well. Let it sit for 10 minutes.
Transfer the shrimp to a cutting board and mince them until chunky but not totally broken down.
In the same bowl, add the minced shrimp, ground pork, chopped pork belly, cooked shiitake mushrooms, soy sauce, rice wine, grated garlic, grated ginger, sugar, salt, black pepper, and cornstarch.
To cook the shitakes, dice, then heat in a bit of oil in a saute pan with 30g/2Tbsp water
Saute until water cooks off, then continue to saute for 1-2 more minutes or until tender and starting to take on color
Mix everything together, then switch to a whipping motion with your hand/fingers. Alternatively, use a stand mixer with a paddle attachment to develop the proteins and create a sticky and heterogeneous filling. Refrigerate until ready to fill your dumplings.