In a medium sized mixing bowl, soak the tamarind in the chicken broth. Set aside. If using lemon juice, skip this step.
Coarsely chop the tomatoes and place in a blender. I had some cherry tomatoes, and wanted to use them, so I set some aside to be added, fresh, at the end. This is optional.
Remove the stem, ribs, and seeds from the chili. Add the flesh to the blender. If you want the soup to be spicy, you can add a few of the seeds to the blender, as well. Otherwise, discard the stem and seeds.
Add the ginger and garlic to the blender.
Wash, dry, then remove the large stems from the cilantro. Save the nice leaves and sprigs, setting them aside. Add the stems to the blender.
Add the sweetener and a bit of salt to the blender. Puree the tomato mixture until fully pureed. If there is not enough liquid to get the blender started, add a bit of the chicken broth (being careful not to get any tamarind seeds).
Heat a medium sized soup pot over medium heat. Add the ghee or coconut oil to the pan.
Once the fat begins to ripple, add the cumin, black pepper, and turmeric. Give the pan a quick swirl, then immediately add the tomato puree to the pan. The brief moment the spices are in the fat will toast them. Do not let them burn.
Stir and break up the tamarind in the chicken or vegetable broth. Use your fingers to smoosh and mix it into the liquid, especially if it contains seeds. Once it is well broken up, strain and push the mixture through a sieve. Add the tamarind broth to the pot, discarding the tamarind seeds and any fibrous material, left behind. If you are using lemon juice, simply add the broth and lemon juice to the pot, at this point.
Turn the soup to low and allow it to simmer for about 20 minutes. Taste it, then adjust seasoning with a bit of salt, if it needs it.
When ready to serve, if you’d set aside any fresh tomato, add it at this point, along with the fresh cilantro leaves and sprigs. Stir this in, then serve!