Place a wok or frying pan over medium-high heat and add the ghee. When it is hot, add the cumin, nigella and carom seeds (if using) and fry until fragrant, about 1 minute.
Next add the ginger and fry for 10–15 seconds, until fragrant, then stir in the tomatoes. Lower the heat slightly, add a splash of water and keep stirring until it starts to simmer. Add the tom