If you can’t find ground ancho chile, you can use the dried peppers. Simply rehydrate one large pepper, puree, and add to the soup with the vegetable stock. Slideshow: Vegetarian Soups
In a large Dutch oven or stock pot, heat the oil. Sauté the onion over medium-high heat until soft, 5 minutes. Add the garlic, cumin, chili powder and 1 teaspoon salt. Cook until fragrant, 2 minutes.
Stir in the black beans and stock, scraping up any brown bits from the bottom of the pot. Bring to a boil and simmer over medium-low heat until the beans are tender and the soup has thickened, 20 minutes.
Remove from the heat and add the lime juice. Taste for seasoning. Serve the soup in bowls and garnish with the sour cream and cilantro leaves.