Slow Cooker Lentil Soup with Sausage and Apples

Time = 30 min prep + 8 hour cook
Servings = 4-6 people
From = NYT Cooking

Ingredients

2 Tbsp unsalted butter
1 large yellow onion, fine chop
2 firm, tart apples (Granny Smith, Honeycrisp) peel and dice 1 apple, reserve 1 apple
3 stalks celary, chopped into 1/2 inch pieces
6 cloves garlic, minced or pressed
1 sprig fresh sage, leaves chopped (can substitute 1/2 tsp dried sage)
1 spring fresh thyme
12 oz dry hard cider (any sparkling or still, dry hard cider works) (see notes)
3/4 pound smoked sausage (kielbasa or andouille), sliced into 1/2 inch coins
10 oz dried small green lentils (French lentils aka lentils du Puy) (see notes)
1/4 tsp ground nutmeg
2 tsp cider vinegar
2 tsp dijon mustard
4 to 6 scallions, thin-slice (garnish)
kosher salt and black pepper (to your taste)

Melt the butter in a large (12-inch) skillet over medium-high heat. Add the onion, season with salt, and cook, stirring, until the onion is translucent, about 5 minutes.
Add half the diced apples and cook, stirring until softened, adjusting the heat as necessary to avoid scorching, about 5 minutes.
Add the celery, garlic, sage and thyme, and stir to combine. Pour in the cider and let it come to a bubble.
Scrape the mixture into a 6- to 8-quart slow cooker. Add the sausage, lentils, nutmeg, 1 teaspoon salt and a generous amount of black pepper to the slow cooker; pour in 3 cups water.
Cover and cook on low heat until the lentls are tender and the flavors have mellowed and blended, approx 8 hours. This soup can hold well on the "keep warm" setting.
Immediately before serving, add vinegar. Combine mustard and sour cream and then stir this into the soup. Taste and adjust salt and pepper as needed.
Serve in bowls topped with scallions and remaining chopped apples.

Watch the liquid as the lentils cook. You may need to top this up with 2-3 cups of water or stock to ensure they remain covered.
If you don’t have time to sauté the onions and apples, you can skip that step, putting the ingredients directly into the slow cooker.
Lentils du Puy have a peppery flavor and keep their shape when cooked. However, you can also use black lentils or brown lentils, but keep in mind that brown lentils will fall apart as they cook, creating a thicker stew.
Any sparkling or still dry hard cider works well in this recipe. In a pinch, you can substitute dry white wine and mix in a few spoonfuls of apple juice, if you have it. For a nonalcoholic option, use chicken or vegetable stock, but increase the vinegar a bit at the end for tartness.