Step 1

In a large Dutch oven or pot, combine the oil, scallions, garlic, cumin, bay leaf (if using), a pinch of salt and one jalapeño half. Set over medium heat and cook, stirring constantly, until scallions are softened and fragrant but not browned, 2 to 4 minutes.

Step 2

Add 5 cups of water, the sweet potato, lentils and 1 1/2 teaspoons salt. Bring to a simmer over medium-high, then reduce heat to low, cover and simmer for 10 minutes.

Step 3

Meanwhile, thinly slice the chard stems all the way to the leaves. Place the stems in a small bowl; add the lemon juice and season with salt. Thinly slice the remaining jalapeño and add to the chard stems to taste. (If you don’t want your soup too spicy, just add a few slices, or leave them out entirely.) Coarsely chop the chard leaves.

Step 4

After the lentils have been simmering for 10 minutes, taste the broth. If flavors are muted, add more salt. If the broth tastes spicy to you at this stage, remove the jalapeño. Add the chard leaves, stir to combine, then cover and cook until the lentils and sweet potato are tender, 8 to 12 minutes. Remove from heat and thin with water if necessary. Remove and discard the bay leaf plus the jalapeño half (if you haven’t already done so).

Step 5

Divide soup among bowls. Top bowls with a spoonful of the chard stems, jalapeño and lemon juice. For a more bracing soup, add another spoonful or two. Soup and topping will keep separately for up to 3 days in the refrigerator. Warm the soup, add water and salt as needed, then combine with the citrusy chard stems.