Black Bean Soup

2 large yellow onions, diced small
2 jalapenos, minced
1 tablespoon extra-virgin olive oil
4 garlic cloves, minced
Coarse salt and ground pepper
2 teaspoons ground cumin
1-3/4 cups low-sodium vegetable broth
1 tablespoon cornstarch
2 tablespoons fresh lime juice (from 2 limes)
Diced avocado, diced onion, cilantro, low-fat plain yogurt, and tortilla strips, for serving (optional)
In a medium saucepan, cover beans with cold water by 2 inches. Add one quarter each of onions and jalapenos and bring to a boil over high. Reduce to a rapid simmer; cook until beans are tender, 45 to 50 minutes.
In a large Dutch oven or heavy pot, heat oil over medium-high. Add garlic and remaining onions; season with salt and pepper. Cook, stirring often, until onions are soft and golden brown, 10 minutes. Stir in remaining jalapenos, cumin, beans and their cooking liquid, and broth. Season with salt and pepper. Bring to a simmer and cook until beans are soft, 20 minutes (if necessary, add up to 1 cup water to keep beans covered).
Transfer 2 cups soup to a blender and add cornstarch. Puree until smooth (use caution when blending hot liquids). Return to pot. Cook, stirring, until soup thickens, 1 to 2 minutes. Add lime juice and season to taste with salt and pepper.
To serve, top with avocado, diced onion, cilantro, yogurt, and tortilla strips if desired.