Heat oven to 400 degrees F.
Lightly salt and pepper the chicken thighs.
Combine 1 tablespoon olive oil, rosemary and the garlic clove in a small bowl. Mix together and brush onto both sides of the chicken.
On the stove top heat a large cast iron skillet (10 inch) or a Dutch oven over medium-high heat. Add the remaining 2 tablespoons of olive oil.
When the oil is rippling on the top place chicken thighs skin side down in the oil. Cook for 5 minutes. Flip over taking care to release the skin from the pan (do not allow the skin to stick and tear off).
Cook an additional 5 minutes. Remove the chicken from the pan.
While the chicken is cooking, in a small bowl combine the cranberries, apple slices, brown sugar and mustard. Toss to combine and coat the fruit.
Combine the chicken stock and apple cider.
Reduce the heat to medium. Slowly pour the liquids into the pan and use a heat proof spatula to deglaze the pan removing any stuck bits of food on the pan. Remove the pan from the heat.
Add chicken back to the pan skin side up.
Spoon the cranberry apple mixture into the pan evenly around the chicken.
Bake in the oven for 20-25 minutes until the chicken reaches 165 degrees internal temperature.
Remove from oven and allow to rest for a few minutes before serving hot.