Curried Sweet Potato and Apple Soup

I almost always crave apples and sweet potatoes in the fall.  Okay, always.  And I love curry, and I love using my mandoline, so I can't wait to try this one out!

Curried Sweet Potato-Apple Soup
3 medium sweet potatoes
3 tablespoons unsalted butter
1 small onion, chopped
2 cloves garlic, smashed
1 2-inch piece ginger, peeled and grated
1/4 teaspoon freshly grated nutmeg, plus more for garnish
1 1/2 teaspoons Madras curry powder
Kosher salt and freshly ground pepper
2 cups low-sodium chicken broth
1 1/4 cups chunky applesauce
1 tablespoon extra-virgin olive oil
1 tablespoon apple cider vinegar
1 to 2 tablespoons chopped fresh cilantro

Preheat the oven to 425 degrees F. Peel and dice 2 1/2 sweet potatoes. Melt 2 tablespoons butter in a large pot over medium heat. Add the onion and garlic and cook until soft, about 5 minutes. Stir in the ginger, nutmeg, 1 1/4 teaspoons curry powder, and salt and pepper to taste and cook until toasted, 1 more minute.

Add the diced sweet potatoes, chicken broth and 2 cups water to the pot, cover and bring to a boil over medium-high heat. Reduce the heat to medium low and stir in the applesauce. Simmer, covered, until the sweet potatoes are soft, about 20 minutes. Puree the soup with a blender until smooth. Season with salt and pepper; keep warm.

Meanwhile, peel and thinly slice the remaining 1/2 sweet potato and toss with the olive oil, and salt and pepper to taste. Spread in a single layer on a baking sheet and bake until crisp, 7 to 10 minutes.

Heat the remaining 1 tablespoon butter in a skillet over medium heat. Add the remaining 1/4 teaspoon curry powder and cook, stirring, until browned; remove from the heat and add the vinegar. Top with the curry butter, cilantro and sweet-potato chips.