When the chillies are very soft, finish making the sauce. Lift the chillies from the saucepan and put them into a small food processor, reserving the simmering liquid. Add 60ml of the simmering liquid and 3 tbsp oil to the food processor. Puree until smooth for 3 to 5 minutes. If the chilli puree isn’t smooth after 5 minutes, strain the mixture through a fine mesh strainer, pressing on the solids to extract as much puree as possible. Discard the solids in the strainer. Season the puree with the cumin, ¼ tsp salt, and ¼ tsp pepper. Transfer 3 tbsp of the chilli puree to a small bowl and set aside for serving.