Preheat oven to 400F and lightly grease a 9x13 baking dish. Melt 2 tablespoons butter in a large high-walled skillet or Dutch oven over medium-high heat. Add onion and celery and saute 3-5 minutes until tender. Add garlic, parsley, poultry seasoning, and sage and saute 1-2 additional minutes until fragrant. Remove pan from heat and allow to cool slightly.
Fold crumbled cornbread into vegetable mixture until evenly combined. Drizzle egg and chicken broth over top, lightly tossing until mixture is moistened. Season stuffing with salt and pepper to taste, transfer to a bowl, and set aside.
Pat chicken breasts dry and cut a slit in each about 2/3 through. Season chicken on both sides with salt and pepper.
Wipe same skillet clean and set over medium-high heat. Add remaining 1 tablespoon butter and vegetable oil to pan and swirl to coat bottom. Add chicken to pan and sear 2-3 minutes per side until golden brown. Transfer to a large plate and set aside for a moment.
Fill each chicken breast with cornbread mixture using toothpicks to secure if needed. Arrange chicken in prepared pan and bake at 400F 15-20 minutes until chicken registers 165F.
Serve chicken breasts warm with gravy on top if desired. Enjoy!
Notes
Storing InstructionsStore chicken in refrigerator up to 6 days. Chicken may also be frozen up to 2 months.