Heat oil in medium stockpot, then add green garlic, mah kwan, white peppercorns, and toast over high heat, then add crab and prawn, continue cooking over high heat for about 5 minutes.

Add chenin blanc, tomatoes, spring onion bottoms, and galangal, reduce by about 1/2, then add water to cover with all remaining ingredients, continue cooking over medium-low heat for about 2 hours, then pass through chinois, continue reduction, adjust as needed, chill, and reserve for service.