The well-caramelized onions that anchor any pot of onion soup pack a powerful sweetness. In the classic recipe, beef broth provides a critical savory counterpoint, but that’s lost in recipes made with vegetable broth, which tends to be a bit sweet itself. To counter that, I use umami-boosting ingredients to simulate a meaty flavor. For these recipes I tested a variety and settled on a combination that included sherry, tomato paste, soy sauce, and, arguably most important, a Parmesan rind simmered in the broth. A touch of sherry vinegar brightens the soup’s flavor noticeably.
VEGETARIAN ONION SOUP
Makes about 2½ quarts
For this recipe, the traditional bread and cheese is prepared and then floated in the bowls of soup. If, however, you serve the soup in broiler-safe crocks, then you can melt the cheese onto the bread right in the bowls. Remember to keep an eye on the cheese so it doesn’t burn. Containers of Parmesan rinds are available at some Whole Foods stores.
Store-bought broth is fine, but if you’re going all out (which, given the 2-plus hours necessary to prep and caramelize the onions, you are), use the homemade broth recipe that follows: It yields a superior soup.
8 cups low-sodium vegetable broth
2 2-inch pieces Parmesan rind
4 tablespoons unsalted butter
5 pounds yellow onions, halved and thinly sliced pole to pole (about 5 quarts, lightly packed)
Salt and pepper
2 bay leaves
1 tablespoon tomato paste
1 tablespoon flour
1 tablespoon minced fresh thyme
½ cup fino (dry) sherry
1½ teaspoons soy sauce
¼ teaspoon sherry vinegar
1 clove garlic, peeled, optional
1½ cups grated gruyere cheese (about 6 ounces), or more, as necessary
2 tablespoons snipped chives, for garnish, optional
In a large saucepan over medium-high heat, bring the broth and Parmesan rinds to a strong simmer. Adjust heat to low, cover the pot, and simmer gently until broth is infused and Parmesan rinds are softened, about 1 hour. Remove the rinds and reserve the broth.
Meanwhile, in a large Dutch oven over medium-high heat, melt 3 tablespoons of the butter. Add the onions and 1 teaspoon salt and cook, stirring occasionally, until the onions begin to release their moisture, about 10 minutes. Adjust the heat to medium, add the bay leaves, and continue cooking, occasionally stirring and scraping the bottom of pot to loosen and dissolve the fond, until the onions are light gold and sticky, 1½ to 2 hours (adjust heat as necessary to prevent scorching; you should have 4 to 5 cups of onions). Meanwhile, fill a measuring cup with ¾ cup water and set aside.
Adjust the heat to medium-low. Add ¼ cup water and scrape the bottom of the pot. Continue to cook, stirring occasionally, until the water evaporates, about 12 minutes longer. Repeat this cooking and deglazing process two more times until all the water has been used and the onions are dark brown. Make a clearing in the onions and add the tomato paste. Cook and stir for about 2 minutes, then blend the tomato paste into the onions. Make another clearing, add the flour and thyme, and continue to cook, stirring occasionally, for about 3 minutes. Then blend into the onion mixture, as with tomato paste.
Adjust the heat to medium-high, add the sherry, and continue to cook, stirring and scraping the bottom of the pot constantly, for about 3 minutes. Add the infused vegetable broth, 1 teaspoon of salt, and pepper to taste, and bring to a simmer, stirring occasionally. Adjust heat to medium-low and simmer, partially covering the pot and stirring occasionally, to blend flavors, about 30 minutes. Remove the bay leaves, add soy sauce, vinegar, and remaining 1 tablespoon of butter, and stir to melt the butter and blend. Taste the soup and adjust seasoning with additional salt and pepper if necessary.
Meanwhile, with the rack in the middle position, heat the oven to 425 degrees. Trim ends off the baguette and bias-cut it into roughly 2-inch-thick slices, 1 to 3 per serving. Arrange the slices on a baking sheet and toast until light gold, about 5 minutes to a side. Heat the broiler and adjust the rack about 6 inches below the element. Lightly rub each toast with the raw garlic clove, if using, sprinkle each evenly with about 2 tablespoons cheese, and broil until the cheese is melted and browned in spots, about 4 minutes. Meanwhile, ladle the soup into warmed serving bowls. Garnish each serving with cheese toasts, sprinkle with some of the chives, if using, and serve at once.
TIP: NO MORE TEARS
ROASTED MUSHROOM-VEGETABLE BROTH WITH PARMESAN ESSENCE
Makes about 2 quarts
Note that you’ll need a roasting pan with deep sides and sturdy handles. Use great care when removing it from the oven, as both the pan and the liquid will be extremely hot.
1 pound button mushrooms, sliced
2 tablespoons neutral oil
1 medium onion, sliced thin
4 ribs celery, roughly chopped
1 carrot, scraped clean and roughly chopped
8 medium garlic cloves, smashed
1 tablespoon tomato paste
3 quarts water, at room temperature
1 small bunch parsley stems
2 2- to 3-inch Parmesan rinds
1½ teaspoons salt
With the rack in the middle position, heat the oven to 475 degrees. In a large roasting pan, toss the mushrooms and 1 tablespoon oil to coat. Roast until the mushroom liquid evaporates, about 20 minutes, stirring once or twice.
Meanwhile, in a medium bowl, toss the onion, celery, carrot, garlic, tomato paste, and remaining 1 tablespoon oil to coat. Add the vegetables to the roasting pan, stir to mix, and continue roasting until they are tender and darkly colored, 35 to 40 minutes, stirring once or twice.
Remove pan from the oven, add about 2 cups of the water, and stir and scrape the bottom of pan to loosen and dissolve the fond. Add remaining water, parsley stems, and Parmesan rinds and stir. Return the pan to the oven, adjust the heat to 550 degrees, and bring the liquid to a simmer. Continue to simmer until liquid has reduced by almost a third, about 15 minutes, stirring once or twice during that time.
Carefully remove the pan from the oven and set aside to cool. Set a strainer over a large bowl and strain the mixture, pressing on the solids to release as much liquid as possible (you should have about 2 quarts). Use in the Vegetarian Onion Soup recipe, or cover and refrigerate for up to 1 week.
FARRO WITH FETA, HERBS, AND ALMONDS
Makes about 8 cups
This can be a hearty meatless side dish for an onion soup supper. Buying feta sold in blocks will make cutting it into cubes a little easier. And I prefer the texture of regular farro over the quick-cooking type.
2½ cups farro (about 15 ounces)
Salt and pepper
2 tablespoons fresh lemon juice, or more, as necessary
1 tablespoon red wine vinegar
1½ teaspoons pressed or grated garlic (about 2 medium cloves)
½ cup extra-virgin olive oil
2 large celery ribs, cut into medium dice (about 1¼ cups)
¾ cup thinly sliced scallion whites and greens (about 6 medium)
½ cup snipped fresh dill, plus small sprigs for garnish
1/3 cup chopped fresh parsley
1 cup slivered almonds, lightly toasted and cooled
6 ounces feta, diced small (roughly ½-inch cubes; about 1½ cups)
In a large saucepan over high heat, bring 2 quarts water to a boil. Add the farro and 1 teaspoon salt, stir, and return to a strong simmer. Adjust heat to low, cover, and simmer until farro is tender but still chewy, about 18 minutes. Drain and set aside to cool.
Meanwhile, in a large nonreactive bowl, whisk the lemon juice, vinegar, garlic, 1 teaspoon salt, and pepper to taste. Vigorously whisk in the oil. Add the cooled farro and 1 teaspoon salt, stir to combine, and set aside for flavors to blend, about 20 minutes. Add the celery, scallions, snipped dill, parsley, and most of the almonds and stir to combine. Add the feta and stir gently to combine (try not to crumble the cubes too much). Taste and adjust the seasoning with salt, pepper, or lemon juice if necessary. Sprinkle with the remaining almonds, garnish with the dill sprigs, and serve.Adam Ried appears regularly on “America’s Test Kitchen.” Send comments to email@example.com.