To mix the sauce, combine the fermented black beans with the Shaoxing wine in a bowl. Let it sit while you prepare the other ingredients so the black beans will soften, 5 minutes or so. Once the fermented black beans turn soft, smash them with the back of a spoon to thicken the paste. It’s fine if you cannot smash the beans evenly and completely. Once done, add the rest of the sauce ingredients and mix well.
Line a large dutch oven or heavy-duty pot with parchment paper and make sure you have about 8” (20cof paper poking out of the pot, so you can wrap up the ingredients later.
Spread the onion onto the bottom of the lined dutch oven. Place the fish on top of the onion, skin-side-down. Arrange the asparagus between the salmon fillets. Pour the black bean sauce over the salmon. Drizzle the olive oil and sprinkle the green onion over the salmon and asparagus.
Fold the paper over to cover the fish and crimp the edges loosely together so it forms a pocket to hold all the ingredients. Add 1/2 cup water outside of the parchment paper, and make sure the water doesn’t enter the paper pocket and dilute the sauce.
Cover the dutch oven with the lid. Cook over medium-high heat until the water boils, 5 minutes or so. Do not uncover the lid during the process. You should hear the water bubble when it starts to boil. Reduce the heat to medium or medium-low. Continue to cook for another 6-10 minutes depending on the thickness of the fish and the doneness you’re looking for. After 6 minutes, uncover the pot and unfold the parchment paper using a pair of tongs (be careful of the hot steam coming out of the pot). Test the doneness of the salmon by inserting a fork into the thickest part of the fillet. It should flake easily and the color should be pale pink throughout. If the salmon is mostly cooked but still has spots of darker pink, cover the pot again, remove it from the stove, and let sit for 3 to 4 minutes. If the salmon doesn’t flake easily, return it to cook on the stove for longer until it’s done.
Once the salmon is cooked, remove the pot from the stove immediately and uncover the pot. Let the steam out for a minute, remove the lid, and carefully open the paper. Transfer the salmon with the onions and asparagus onto a serving plate. Transfer the remaining sauce as much as possible onto the salmon using a spoon.
Serve hot with steamed rice as a main dish.