2.Quarter remaining four onions then blend or process with chili, juice and half of the oil until chopped coarsely; add nuts, blend or process until mixture is chopped finely.
3.Heat remaining oil in medium frying pan; cook shrimp paste, stirring, about 1 minute or until fragrant. Add coconut milk, tamarind, sugar and processed onion mixture; bring to a boil then reduce heat. Simmer, uncovered, stirring occasionally, about 4 minutes or until sauce thickens slightly.
4.Stir in finely chopped onion off the heat.
If shrimp paste is unavailable, substitute 1 tablespoon fish sauce. Shrimp paste is available from Asian grocery stores or the Asian section of most supermarkets. Tamarind concentrate is made from dried tamarind pulp and is a popular souring agent that adds an appetising tang and fruity background flavour to curries and sauces