Pre-heat a skillet over medium-high heat. Add the olive oil and butter sear chicken breast until nicely browned, about 6 to 8 minutes on each side. Remove chicken from the pan and cover with foil.
Add the shallots and crushed garlic to the skillet and sauté for a few minutes, until lightly browned. Add the balsamic vinegar and deglaze the pan by scraping up any brown bits on the bottom of the pan. Add the honey, brown sugar and mustard. Bring the mixture to a boil for 2 to 3 minutes, until the sauce starts to reduce and thicken. Add the chicken stock and tomatoes and gently simmer over medium heat for 5 to 10 minutes.