Heat oil in a frying pan over medium heat. Fry shallots and garlic until crisp and fragrant. Divide into 2 portions and set aside. Cut off the ends of the cabbage bunches and discard. Rinse leaves and drain well. Set aside.
Place 1 portion of fried shallots and garlic into a pot. Add stock and bring to the boil over high heat. Add prawns and cabbage and cook for 3–5 minutes or until prawns are cooked. Drain prawns and cabbage and set aside.
Add vermicelli to stock and cook for 1–2 minutes. Remove from heat, then divide among prepared serving bowls. Arrange prawns, cabbage, fried shallots and garlic on top of noodles. Drizzle with a little sesame oil and serve immediately.
Cook this dish just before serving, as wheat flour vermicelli tends to absorb the stock very quickly. Even leaving the dish stand for less than 5 minutes will cause the vermicelli to become soggy.
Combine all ingredients in a large pot and bring to boil over medium heat. When mixture boils, reduce heat to low. Leave to simmer for about 40 minutes to 1 hour. Remove from heat and strain before use. If not using immediately, store in an airtight container 3 days, or freeze for up to a month. Makes about 1.5 Litres.
Alternatively, use 4 seafood stock cubes.