Place the chicken in a 6-quart slow cooker. Drizzle with ¼ cup of the hot sauce, tossing to coat. Dot chicken with 1 tablespoon butter.
Rub 1 teaspoon melted butter onto the skin of the sweet potatoes.
Arrange the sweet potatoes evenly on top of the chicken.
Cover and cook on high for 4 hours or low for 6, or until the chicken is cooked through and the sweet potatoes are tender.
While the chicken and sweet potatoes cook, make the sauce by whisking together the yogurt, lime juice and salt. Refrigerate if making ahead.
Carefully remove the potatoes from the slow cooker--they will be very soft so you may need to use tongs and a spatula--and set aside.
Remove the chicken and shred with two forks. Return the chicken to the slow cooker, stirring together with any accumulated juice. Pour in the remaining ¼ cup hot sauce, stirring to combine.
Slice the sweet potatoes lengthwise, top with the shredded chicken and accumulated juices. Top with white sauce if using, and serve.
