Prepare the Ingredients: Place 500g pork ribs in a bowl and cover with cold water. Soak for 30 minutes, changing the water once or twice. Meanwhile, wash and cut 3-4 tomatoes into 2 cm cubes. Cut 1-2 corn cobs into 3-4 cm segments. Peel and cut 1 potato into chunks, placing them in a bowl of water to prevent browning. Clean 3 mushrooms, remove the stems, and score the tops with a cross.

Blanch the Ribs: Drain the ribs and place them in a pot. Cover with cold water by 2 cm. Add 1 scallion segment, the sliced ginger, and 2 tsp cooking wine. Bring to a boil over high heat. As grey foam rises to the surface, skim it off carefully with a spoon. Continue boiling for 1 minute after skimming, then drain the ribs and rinse them thoroughly with warm water.

Sauté the Base: In a clean pot, heat 10 ml cooking oil over medium heat. Add the chopped tomatoes and cook, pressing them with your spoon, for 3-4 minutes until they break down and become saucy.

Combine and Simmer: Add the blanched ribs to the pot and stir for 2-3 minutes to coat them. Pour in enough boiling water to cover all ingredients by 1-2 cm. Add the corn segments, potato, and mushrooms. Bring to a boil, then reduce the heat to low, cover, and let it simmer gently for 1 hour.

Season and Serve: Season the soup with 4-6 g salt, 1 tsp light soy sauce, and 1 tsp oyster sauce. Stir gently to combine. Taste and adjust seasoning if necessary. Turn off the heat, stir in the chopped scallions, and serve immediately.