When the split peas are cooked, whisk them to the consistency of a bisque. Add more water to thin it down or boil it to reduce it. Season with salt.
To season, garnish and serve the soup, dry roast the cumin seeds in a small pan until they darken a few shades. Add the remaining butter , cilantro or parsley. When warm, stir the seasoning into the soup. Ladle the hot bisque into shallow large bowls, swirl the mango puree over the top, and sprinkle with raw sugar.