• 8 cm (3¼ inch) piece lemongrass, white part only, very finely chopped
• 4 cloves garlic, thinly sliced
• 3 cm (1¼ inch) piece ginger, thinly sliced
• 2 teaspoons salt
• 2 tablespoons vegetable oil
• 8 cm (3¼ inch) piece rampe (pandanus) leaf*
• 1 teaspoon cumin seeds
• 1 teaspoon mustard seeds
• ½ teaspoon fenugreek seeds
• 1 cinnamon stick
• 1 teaspoon unroasted chilli powder*
• 1½ teaspoons roasted curry powder (store-bought)
• 1 teaspoon ground turmeric
• 1 teaspoon ground coriander
• 1½ tablespoons coconut vinegar* (or rice vinegar)
• 1 tablespoon tomato ketchup
• 300 g (10½ oz) tinned tomatoes, puréed

Using a mortar and pestle, pound the lemongrass, garlic, ginger and salt into a paste. Heat the oil in a saucepan over low-medium heat and fry the paste with the rampe, cumin and mustard seeds for 3 minutes, stirring regularly so the paste doesn’t stick to the bottom of the pan.

Add the fenugreek seeds, cinnamon stick, chilli powder, curry powder, turmeric and coriander and cook for 1 minute. Add the coconut vinegar and 250 ml (9 fl oz/1 cup) water and bring to the boil, then reduce the heat to low-medium and simmer for 10 minutes.

Remove from the heat and strain through a fine sieve into another saucepan, discarding the solids. Return the liquid to the stove, and add the tomato ketchup and tomatoes. Bring to the boil, then simmer over low-medium heat for 15 minutes, or until the sauce has thickened. Allow to cool to room temperature before serving.