In a food processor or by hand, finely chop the carrot, fennel, celery, cilantro, garlic and ginger.

In a large pot, heat the oil and then add the coriander and cumin, stirring to “bloom” or toast the spices until they’re very fragrant, being careful not to let them burn.

Add the chopped vegetables, then the cilantro stems, and then the red lentils and salt and pepper. Stir to combine, add water to cover and cook over medium heat, stirring occasionally to prevent burning. As the lentils absorb the water, add more, until you’ve added all 3 quarts.

Simmer until lentils go from red to yellow and are completely soft, about 45 minutes.

Remove from heat, add cilantro leaves (reserving a handful for garnish) and, when cool enough to handle, puree with immersion blender (or in a traditional blender in batches) until smooth, thinning with more water if needed.