Lentil Soup with Smoked Sausage and Apples

• 2 tablespoons unsalted butter
• 1 large yellow or red onion, finely chopped

Kosher salt and black pepper

• 2 tart-firm apples, such as Honeycrisp, peeled and diced
• 3 celery stalks, chopped into 1/2-inch pieces
• 6 garlic cloves, finely chopped
• 1 fresh sage sprig, leaves chopped, or 1/2 teaspoon dried sage
• 1 fresh thyme sprig, leaves chopped, or 1/2 teaspoon dried thyme
• 1 ½ cups/12 ounces dry hard cider
• ¾ pound smoked sausage, such as kielbasa or Andouille, sliced into 1/2-inch-thick coins
• 1 ½ cups/10 ounces dried small green lentils (also called French lentils or lentils du Puy)
• ¼ teaspoon ground nutmeg
• 2 teaspoons cider vinegar
• ¼ cup sour cream
• 2 teaspoons Dijon mustard
• 4 to 6 scallions, thinly sliced for garnish

1. Melt the butter in a large Dutch oven over medium-high heat. Add the onion, season with salt, and cook, stirring, until the onion is translucent, about 5 minutes. Add the half the chopped apples, and cook, stirring until softened, adjusting the heat as necessary to avoid scorching, about 5 minutes.
2. Add the celery, garlic, sage and thyme, and stir to combine. Pour in the cider and let it come to a bubble. Add the sausage, lentils, nutmeg and 4 cups water to the pot. Season with 1 teaspoon salt and a generous amount of pepper. Let the soup come to a boil, then decrease the heat to maintain a low simmer. Cover the pot and cook until the lentils are tender, 35 to 40 minutes.
3. Just before you are ready to eat, add the vinegar. Stir together the sour cream and mustard, then stir the mixture into the soup. Taste and add more salt and pepper if necessary. Serve in bowls topped with the scallions and remaining chopped apples.