Soften the onions – Heat the oil in a large pan over medium heat, then add the onions and salt. Cook the onions gently for about 20 minutes, stirring occasionally, until they become soft and slightly golden.
Add aromatics and spices – Stir in the garlic and ginger, cooking for another minute or two. Next, sprinkle in the garam masala, coriander, cumin, paprika, turmeric, cinnamon, and black pepper. Stir everything well and allow the spices to cook for another couple of minutes.
Incorporate the vegetables – Add the carrot, cabbage, peppers and tomatoes. Stir well to ensure everything is evenly mixed.
Simmer with stock – Pour in the stock and bring everything to a gentle boil. Reduce the heat and let it simmer uncovered for around an hour, allowing the vegetables to fully soften and the flavours to develop.
Blend until smooth – Once cooked, allow the mixture to cool slightly before blending it into a smooth consistency using a stick blender or a jug blender. The finished texture should be similar to a thick soup.
Prepare for use – When adding this to curries, the base gravy should be heated and thinned with a little water if necessary, ensuring it reaches the consistency of a light sauce. Keeping it warm before adding to a curry will help maintain the right cooking temperature.