In a skillet over medium-high heat, add the olive oil and ghee.
While the ghee is melting, season the chicken with salt and pepper to taste.
Add the chicken, skin-side-down, and sear both sides until golden brown. Set the chicken aside.
Grease the slow cooker pot with cooking spray, and place the sweet potatoes into it.
Stir in the garlic and rosemary, and season with salt and pepper.
Add the chicken to the slow cooker in an even layer.
Cover and cook on low for 3-4 hours.
If you think your sweet potato is already cooked after 2-3 hours, remove the sweet potato to avoid it becoming soggy. Continue cooking the chicken for one hour more or until it is cooked through. The chicken is cooked when it reaches an internal temperature of 165ºF.