Sweet Potato Broth

By JOE YONAN The Washington Post

Posted Feb 17, 2015 at 12:01 AM Updated Feb 17, 2015 at 1:00 PM

Food trends seem to come at the speed of light nowadays. You hear somebody mention the words “bone broth,” and you think, “Isn’t that just stock?” The next day you hear it mentioned about a dozen times on Twitter, and you read a piece emphasizing that it’s so much more than just stock, and the day after that you hear a story about it on the radio explaining that it has to include vinegar, and you spot it on a restaurant menu and see it in little aseptic packages in the supermarket.

A little part of you continues to think, “Isn’t it just stock?” and wishes everybody would just shut up about it, already. And the whole thing reminds you of why you don’t listen to commercial music radio anymore: Some perfectly catchy tune is reduced to the most annoying earworm ever just because some DJ has no imagination.

Anyway, I don’t think that’s going to happen with another broth I discovered recently. I was flipping through “Soul Food Love,” Alice Randall and Caroline Randall Williams’ new cookbook, looking for ideas, and I saw the most beautiful soup, made of sweet potatoes, kale and black-eyed peas. But the sweet potatoes weren’t in big chunks, like the carrots. They had been pureed with a lot of water, making a beautiful orange backdrop for the chunky soup.

The three words I read next made me gasp out loud: sweet potato broth. The story is that Alice needed a vegetarian substitute for her classic soup, and she and her daughter, Caroline, came up with the sweet potato idea. It’s simple enough: You simmer a cut-up sweet potato with aromatic vegetables and water -- and some whole cloves -- until the potato is tender. Then fish out those cloves and puree the rest.

When you use it to make the soup -- and substitute collards or mustard greens for the kale, if you like, you realize the true brilliance: The broth is thin enough to let the other ingredients take center stage but thick enough to provide just the right amount of body. The recipe makes more than twice as much broth as you need for the soup, but consider it a bonus, because there are lots of other ways I can imagine using the broth. One night, I’ll make a vegetarian riff on tortilla soup, with black beans and tomatoes.

Sweet potato broth deserves to be trendy, but it probably never will be. And that’s fine with me, because I don’t ever want to get sick of it.

SWEET POTATO, COLLARD AND BLACK-EYED PEA SOUP

This cold-weather soup starts with a brilliant base: a vegetable broth made from sweet potatoes, which are cooked and pureed to yield broth with a lovely color and body previously found only in meat stocks.

The recipe makes 10 cups of broth, but you will need just 4 to 5 cups for the soup, so refrigerate or freeze the rest for another use.

Make ahead: The sweet potato broth and finished soup can be refrigerated for as long as 5 days or frozen for as long as 2 months.

For the sweet potato broth:

1 tablespoon extra-virgin olive oil

1 medium onion, thinly sliced

3 celery ribs, chopped

1 medium carrot, scrubbed, trimmed and chopped

1 large sweet potato (about 1 pound), peeled and cut into large chunks

6 cups water

5 whole cloves (can substitute 2-3 whole star anise)

1/2 teaspoon fine sea salt, and more as needed

1/2 teaspoon freshly ground black pepper, and more as needed

For the soup:

1 tablespoon extra-virgin olive oil

1 large onion, cut into 1/4-inch dice

1 rib celery, cut into 1/4-inch slices

1 large carrot, scrubbed, trimmed and cut into 1/4-inch coins

3 cloves garlic, finely chopped

Leaves from 5 sprigs fresh thyme

1 tablespoon dried thyme

1/4 teaspoon crushed red pepper flakes, and more as needed

14-1/2 ounces canned, no-salt-added diced tomatoes, and juice

2 bunches (8 cups) collard greens, stemmed and torn into bite-size pieces (can substitute kale or mustard greens)

30 ounces canned, no-salt-added black-eyed peas, rinsed and drained

1/2 teaspoon fine sea salt, and more as needed

For the sweet potato broth: Heat the oil in a large stockpot over medium-low heat. Stir in the onion, celery and carrot to coat; cover and cook until the onion has softened, about 8 minutes. Add the sweet potato, water, cloves, salt and black pepper. Increase the heat to medium-high; once the mixture comes to a boil, reduce the heat to medium or medium-low, so the liquid is barely bubbling. Cook, uncovered, until the sweet potato is very soft, about 30 minutes. Discard the cloves.

Use an immersion blender to puree until smooth. Alternatively, transfer cooked broth in batches to a blender or food processor, removing the center knob of the blender lid so steam can escape and holding a towel over the opening; puree until smooth. Taste, and adjust the seasoning as needed.

For the soup: Heat the oil in a stockpot over medium heat. Stir in the onion, celery and carrot to coat; cook, stirring frequently, until the vegetables just begin to soften, about 5 minutes. Stir in the garlic, fresh and dried thyme, and crushed red pepper flakes, then pour in 4 cups of the sweet potato broth, along with the tomatoes and juice. Increase the heat to medium-high.

Once the mixture comes to a boil, stir in the collard or other greens. Reduce the heat to medium or medium-low so the liquid is barely bubbling around the edges. Cover and cook until the greens are tender, 40 to 45 minutes.

Add the black-eyed peas; cover and cook for 10 to 15 minutes, so the flavors meld. If the soup seems too thick, add broth or water to reach your desired consistency. Season with the salt; taste, and adjust with more salt or crushed red pepper flakes as needed. Serve hot.

Makes: 12 servings

Nutrition per serving: 90 calories, 5 grams protein, 15 grams carbohydrates, 3 grams fat, 0 grams saturated fat, 0 milligrams cholesterol, 170 milligrams sodium, 5 grams dietary fiber, 3 grams sugar

-- Adapted from “Soul Food Love,” by Alice Randall and Caroline Randall Williams (Clarkson Potter, 2015).