Slow Cooker Sweet Potato and Lentil Soup

Serves 4
1 large sweet potato, peeled and diced
3 medium carrots, cut into 1/2-inch pieces
3 stalks celery, cut into 1/2-inch pieces
2 leeks, halved lengthwise and cut into 1/2-inch pieces (white and light green parts only)
3/4 cup dried yellow or red lentils
1 4 -inch piece ginger, peeled and finely grated
1 teaspoon curry powder
Kosher salt
1 tablespoon unsalted butter
2 cloves garlic, thinly sliced
Juice of 1/2 lemon, plus lemon wedges for serving (optional)
1/2 cup chopped fresh cilantro
Directions
Combine the sweet potato, carrots, celery, leeks, lentils, ginger, 3/4 teaspoon curry powder and 1 teaspoon salt in a 4-to-6-quart slow cooker. Add 6 cups water and stir, then cover and cook on low, undisturbed, 8 hours. Stir the soup vigorously with a whisk to make a rough puree. Thin with hot water, if desired. Melt the butter in a small skillet over medium-high heat. Add the garlic and the remaining 1/4 teaspoon curry powder and cook until the curry powder is slightly toasted, about 1 minute. Stir the curry mixture into the soup and add the lemon juice, cilantro, and salt to taste. Serve with lemon wedges.
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