Chicken curry with apples and raisins

Ingredients
1 medium yellow onion, sliced
1 tablespoon extra-virgin olive oil
1 tablespoon curry powder, divided
4 boneless, skinless chicken breast halves
1/2 teaspoon kosher salt
1/2 teaspoon freshly ground black pepper
1/2 pound small red potatoes, quartered
1 large tart cooking apple, chopped
1/3 cup golden raisins
1 cup sour cream
2 tablespoons fresh cilantro, minced

Directions
In a small skillet, sauté the sliced onion in the olive oil on medium heat, about 7 minutes. Season with 1 teaspoon of the curry powder.
Season the chicken with the remaining curry powder, salt, and pepper.
Place the potatoes, apple and raisings in the slow cooker, and add the seasoned chicken and onions.
Cover; cook on Low for 6 to 8 hours (or on High 3 to 4 hours).
Prior to serving, remove the chicken and potatoes and set aside, covering to keep warm.
Add the sour cream to the remaining juices in the stoneware, whisking until smooth. Cook on High for 10 minutes or until warmed throughout.
To serve, spoon the sour cream sauce over the chicken and potatoes and garnish with the cilantro.