Heat the oil in a frying pan, sauté onion, garlic and ginger and cook for 4 minutes.
Add pumpkin and wine and boil,uncovered, until wine is reduced by about half. Stir in stock and simmer, covered, until pumpkin is tender.
Heat 1t oil in frying pan over a high heat and sauté lemon grass and chillies to taste, stirring, until lightly browned. Remove from heat.
Purée pumpkin mixture in batches and return to pot. Stir in lemon grass mixture, bay leaves, lemon juice, fish sauce and sugar. Simmer uncovered for 20 minutes.
Pour soup through a sieve, discarding solids, and season well with salt and pepper.
Serve in soup tureen or small hollowed out pumpkins.