Season the chicken breasts to taste with salt and pepper. Melt 1 tablespoon of butter in a large skillet over medium heat. Sear, and cook until browned on both sides and the juices run clear, about 10 minutes. Remove chicken and keep warm.Advertisement
Melt remaining 1 tablespoon of butter in skillet; stir in onion and cook until translucent, 3 to 4 minutes. Pour in red wine vinegar, orange juice, and chicken broth; increase heat to medium-high, and bring to a boil. Stir in the cornstarch and water mixture, and cook until the sauce thickens and turns clear, 1 to 2 minutes. Reduce heat to medium, and stir in the raspberries and orange segments; cook for 2 minutes until softened. Add the chicken breasts to the sauce, and cook to reheat. Serve chicken with sauce spooned over it.