Sauté the Aromatics: In a large soup pot or Dutch oven, warm the olive oil over medium heat. Once shimmering, add the chopped onions, diced celery, and carrot slices. Sprinkle lightly with salt to help the veggies release moisture. Cook, stirring occasionally, for about 10–15 minutes, until the vegetables are softened and aromatic.
Infuse with Spices: Stir in the minced garlic, ground cumin, and crushed red pepper flakes. Cook for about 30 seconds, just until the spices are fragrant and the garlic is golden—but not browned.
Simmer the Soup Base: Add the rinsed black beans and vegetable broth to the pot. Stir well and bring the mixture to a gentle boil over medium-high heat. Once boiling, reduce the heat and let it simmer uncovered for 30 minutes. This allows the flavors to deepen and the beans to become ultra-tender.
Blend for Creamy Texture: Carefully ladle about 4 cups of the soup into a high-powered blender. Blend until smooth, allowing steam to escape if necessary. Alternatively, you can use an immersion blender directly in the pot to partially blend the soup, leaving some texture. Return the puréed portion to the pot and stir to combine.
Finish and Serve: Turn off the heat and stir in the chopped cilantro (if using), vinegar or lime juice, and season with salt and pepper to taste. Adjust acidity and seasoning based on your preference. Serve hot with your favorite toppings like avocado, tortilla chips, or radish slices.