Vietnamese spring onion oil (Mỡ hành)

1. Wash the spring onions and dry them thoroughly – water will make the oil spit.

2. Slice thinly and put into a heatproof bowl with the salt and sugar.

3. Heat the oil in a small pan until a slice of onion dropped in sizzles immediately.

4. Carefully pour the hot oil over the spring onions – they will sizzle and turn bright green.

5. Stir and leave to cool.

6. It keeps in a clean jar in the fridge for a week; stir before using.

Tip: A simple but essential Vietnamese topping, spooned over grilled meat, rice noodles, bánh bột lọc or plain rice. For a richer, more traditional flavour, replace some of the oil with melted lard.