This is from Deborah Madison's Vegetable Literacy. Smaller, tender chard leaves are best (says Madison), but I used giant ones and it was still delicious. Don't worry about chopping too precisely during prep, because this is all going into a blender when it's done.
8 cups packed trimmed chard leaves (about 1 pound or 20 leaves)
2 to 3 tablespoons olive oil
1 onion, sliced
1 small potato (about 4 ounces), scrubbed and sliced
1 carrot, scrubbed and sliced
2 tablespoons tomato paste
1.5 teaspoons ground cumin
1 teaspoon ground coriander
Finely cut cilantro stems and leaves to make 1 cup
1/2 cup sour cream or yogurt
Freshly ground pepper
Grated zest and juice of 1 lime
Rinse the chard, chop it coarsely, and set aside in a colander to drain.
Heat the oil in a soup pot over medium heat. Add the onion, potato, and carrot and cook, stirring occasionally, for about 5 minutes to soften. Stir in the tomato paste, smashing it into the vegetables, and then add the cumin, coriander, cilantro, and chard leaves. Sprinkle over 1.5 teaspoons salt, cover the pan, and allow the leaves to cook down substantially before adding 5 cups water. Bring to a boil, then lower the heat to a simmer, cover partially, until the potato has softened.
Cool slightly, then add the sour cream and puree in a blender until smooth. Return the soup to the pot over gentle heat. Taste for salt, season with pepper, and stir in the lime zest and juice. Ladle into bowls and serve.
With Texture: Add cooked rice, crisped coarse bread crumbs, or skinny tortilla strips to each serving.
With Other Greens: In spring and early summer, include other greens, such as tender sorrel leaves, wild nettles, lovage leaves, lamb's-quarters, and so on.