Marinate the Chicken (Optional): Season chicken breasts with salt, pepper, and rosemary. If desired, marinate for 1 hour in the refrigerator for deeper flavor.
Sear the Chicken: Heat olive oil in a skillet over medium-high heat. Add chicken breasts and cook for 4-5 minutes on each side until golden brown. Remove and set aside.
Prepare the Sauce: In the same skillet, add garlic and sauté until fragrant (about 1 minute). Pour in bourbon, scraping the pan to deglaze. Simmer for 2 minutes to reduce the alcohol.
Add Sweetness: Stir in blackberries, honey, and balsamic vinegar. Simmer for 8-10 minutes, crushing the berries slightly to release their juices and form a rich glaze.
Cook the Chicken: Return the chicken to the skillet, coating it with the sauce. Simmer for an additional 10-12 minutes, ensuring the chicken is cooked through (internal temperature: 165°F/75°C).
Finish and Serve: Optionally, stir in butter for a glossy finish. Serve hot, garnished with extra blackberries and fresh rosemary.