Step 1

Heat the olive oil in a large Dutch oven or heavy pot over medium heat. Add the onion, celery, bell pepper and carrot. Cook, stirring occasionally, until the vegetables begin to soften, 5 to 7 minutes. Season with 1 teaspoon salt and the red pepper flakes.

Step 2

Make a space in the middle of the pot and add the tomato paste, garlic, smoked paprika and coriander. Cook this mixture in that spot, stirring, until the tomato paste darkens a shade or two, about 1 minute, then stir into the vegetables. Add 12 cups water and the bay leaves. Bring to a rapid simmer and cook until the liquid has reduced slightly, about 15 minutes.

Step 3

Add the sweet potatoes and black beans. Continue to simmer rapidly until the vegetables are very tender and the soup is thick and flavorful. 20 to 30 minutes more. Remove and discard the bay leaves. Stir in the parsley. Season with additional salt, as needed. Ladle into soup bowls and serve with a drizzle of olive oil and 3 to 4 drops of sherry vinegar per bowl if using.