Preheat oven to 220°C. In a medium bowl, add sweet potatoes, apples and chopped rosemary. Season with salt and freshly ground black pepper, drizzle with 1 tbsp olive oil and toss to coat.
In a large ovenproof skillet add olive oil and heat over a medium-high heat. Add chicken thighs skin-side down and sear for 5 minutes or until golden-brown and crispy. Set aside.
In the same skillet, add apple cider, honey and Dijon mustard and deglaze the bottom of the pan. Cook for 5-10 minutes or until the mixture has slightly thickened and it coats the back of a spoon. Add the butter and the sweet potato mixture, tossing.
Return the chicken thighs to the skillet, skin-side up. Add fresh rosemary sprigs and transfer skillet to the oven.
Roast for 20 minutes or until the chicken reaches an internal temperature of 74°C and the sweet potatoes are tender. If the potatoes need longer to cook, take out the chicken thighs and continue cooking until tender.