Rinse dried shiitake mushrooms then soak them in 2 cups (500ml) of water for about 6 hours or overnight (If in a hurry, soak in hot water for 30 minutes). Take them out (Keep the water in which they’re soaked for later use) and trim off the stems then cut into thin slices.
Soak dried shrimp in ¼ cup (60ml) of hot water for about 10 minutes. Chop it into smaller pieces. Keep the soaking water.
Prepare other ingredients
Cut tofu into bite-sized cubes. Slice tomatoes into wedges. Separate the stems and leaves of bok choy. Cut them into 1-inch (2½ cm) pieces. Finely chop the scallions, and keep their white and green parts separated.
Cook the soup
Heat cooking oil in a wok (or a pot). Sizzle the white part of the scallions and dried shrimp until fragrant. Stir in the mushroom and tomato. Fry briefly until the tomato becomes a little mushy on the edge.
Slowly pour in the water in which the mushrooms are soaked, leaving any impurities at the bottom of the bowl. Add the dried shrimp soaking water and 2 cups (500 ml) of hot water. Bring it to a full boil.
Slide in the tofu cubes. Leave to simmer over medium heat for 2 minutes.
Add the stem part of the bok choy. Cook for a further 20 seconds.
Turn off the heat. Stir in the leafy part of the bok choy. Add light soy sauce, salt, white pepper, and sesame oil. Mix well then garnish with the green part of the scallions.
Notes
1. If dried shiitake is unavailable, use fresh shiitake, or other flavorful mushrooms. In this case, you can use chicken, mushroom, or vegetable stock, instead of water, to enhance the flavor.2. To make this dish vegan-friendly, skip dried shrimp and use vegetable stock to compensate.