Using a cast iron skillet, heat olive oil over medium-high heat. Add chicken thighs seasoned with salt and pepper.
Add chicken thighs to skillet and cook for 5-6 minutes and then flip over and cook another 2 minutes. Transfer chicken to a plate.
Add the onion wedges and apple chunks to the skillet. Cook in skillet for 5 minutes.
Meanwhile, mix the chicken broth and honey mustard in medium-sized bowl and pour over the onion and apple mixture. Bring contents to a boil.
Return the chicken thighs to skillet and bake in the oven for 15-20 minutes until chicken reaches internal temperature of 165 degrees.
Gravy:
Upon removing chicken from the oven, transfer thighs to a plate. Simmer the remaining juices over medium heat. Mix butter and flour together and gradually add to chicken juices and stir well. Pour over chicken and serve.