Place the garlic, ginger, coriander, 1 tbsp oil and chili into a blender and blend into a smooth paste.
Place a large pan over a medium heat, add the paste, onions and the aubergine and cook until the vegetables are soft and slightly golden.
Add the cardamom pods, cumin seeds, garam masala, coriander seeds, cinnamon stick and black peppercorns to the pan and cook for a further 5 minutes.
Add the lemon juice, the chopped tomatoes and the vegetable stock.
Cook on a low heat for 10 minutes or until desired consistency.
Take off the heat, remove the cinnamon stick and serve.