It's a well-known fact that everything is better when you stuff it (at least when it comes to food). The inspiration for this recipe is rooted in that undeniable truth and the fact that Brie and apples are nothing if not delicious. I hope you enjoy this as much as I did.
Heat 1 tablespoon of the olive oil in a skillet over low to medium heat. Add the chopped onion and cook until tender, stirring often, about 5 minutes. Once the onions are soft and slightly browned, add the chopped apple, 1/2 the salt, 1/2 the pepper, and the hard apple cider. Cook, stirring frequently, until apples are somewhat tender, about 6-7 minutes. Pour the mixture into a bowl and let cool for about 7-10 minutes. Once it's cool, stir in the Brie.
Preheat the oven to 375 degrees.
Heat the remaining olive oil in the same skillet over medium-high heat. Season the chicken breasts with the rest of the salt and pepper and add to skillet. Brown each side for 1-2 minutes and remove from heat. Slice the inside of each breast to make a pocket. Stuff the pocket with the Brie, apple, and onion filling. Don't worry about over-stuffing — the more the better and it's OK if some falls out! Place the stuffed chicken breasts in the oven and bake 35-45 minutes until chicken is cooked through. Remove from oven, serve, and enjoy!