Preheat oven to 425 degrees.
In a small bowl, whisk together mustard, syrup, and vinegar.
Place chicken breasts into 9x13 lined baking dish. Season with salt & lots of pepper.
Pour mustard mixture over chicken. Make sure each breast is coated. Put some more pepper on, if you please.
Bake for 30-40 minutes, or until meat thermometer reads 165 degrees.
Season with fresh rosemary.
