To prepare sea cucumber, use a clean toothbrush to wash the dirt. Soak in clean water for 24-36 hours, changing water every 12 hours.
When it is softened, use scissors to cut along the crack near the belly of the sea cucumber to open. Use scissors to cut each of the internal ribs into 3 and 4 segments along their length. This rib is very nutritious and should not be removed. Rinse to remove the inside dirt.
Pour in pure water to submerge the sea cucumbers in a saucepan, making sure the pan is completely oil-free and salt-free. Cook until it reaches your desired softness, about 20 minutes. Then turn off the heat and allow the water in the pan to cool naturally. Change the water and let it soak for another 48-72 hours, changing water every 12 hours. After all, the sea cucumbers have gained greatly in size.
To make dashi stock, soak 20gcdried kelp in 1.5 liter water in a clean jar overnight in the refrigerator. Also clean and soak dried shiitake mushroom in cold water in a clean jar overnight in the refrigerator.
Combine the kelp and shiitake water in a saucepan and bring to a boil. Remove the kelp before it comes to a full boil. Do not boil the kelp as it will turn slimy and bitter when cooked under high temperature. Continue to cook the shiitake mushroom for 1 minute and remove. Line a mesh strainer with parchment paper to strain the dashi stock.
Cut the rehydrated sea cucumber & shiitake mushroom into bite-size pieces.
Bring the strained dashi stock back to a boil and add the vegetables. Carrots first, then garlic and ginger, mushroom, baby corns. Add the softer sea cucumbers later. Cook 15-20 minutes till soft. Then season to taste with soy sauce and salt.