On medium heat in a large pot heat oil and add curry paste and toast and stir until aromatic. Add onions, lemon grass and garlic and chicken and lightly brown in curry oil mixture. Add coconut milk and shaved chocolate and stir until chocolate is dissolved. Add kaffir lime leaves and all the basil stems and simmer until chicken is cooked and curry tastes good. Season with fish sauce and lime juice to taste.
Garnish with basil leaves. Serve with toasted bread or steamed rice.