Thai-style aubergine curry

Name: Thai-style aubergine curry
Prep time: 30 min
Cook time: 1 h
Total time: 1 h 30 min
Cuisine: Asian, Thai
Ingredients: 5 tbsp sunflower oil; 2 aubergines, cut into batons 2cm/¾in thick; 1 onion, peeled and quartered; 4 garlic cloves, peeled; 3cm/1¼in piece fresh root ginger, peeled; 2 sticks lemongrass, tough outer leaves removed, roughly chopped; 5 cardamom pods; 1 tbsp cumin seeds; 1 tbsp coriander seeds; 1 tsp ground turmeric; ¼ tsp ground nutmeg; 1 tbsp caster sugar; 3 tbsp peanut or cashew butter; 1 x 400ml tin coconut milk; 250ml/9fl oz chicken stock or vegetable stock; 1 fresh red chilli, seeds removed, sliced; 150g/5½oz fresh spinach, washed; 2 tbsp fish sauce or vegetarian fish sauce; 1 tbsp fresh lemon juice; small handful Thai basil leaves; sea salt; cooked rice, to serve