Start by heating olive oil in a large pot over medium heat.
Add the chopped onion and minced garlic, sautéing until they're tender and fragrant.
Pour the black beans and vegetable broth into the pot with your aromatic mixture.
Add cumin and cayenne pepper, stirring well to combine all ingredients.
Blend about one quart of the soup using a blender until smooth.
Pour back into the pot for a thicker texture and enhanced flavor.
In a separate bowl, stir the cornstarch and water together until smooth.
Add this mixture to the soup, increasing the heat and bringing it to a boil for about a minute.
Once boiled, lower the heat to simmer and season with salt and pepper.
Add chopped cilantro just before serving for a fresh kick.