2 lbs – 2 1/4 lbs boneless skinless chicken breast halves (4 – 6 medium chicken breasts)
1/4 cup whole grain, coarse mustard
2 Tbsp dijon mustard
2 Tbsp yellow mustard
1/4 cup + 2 Tbsp honey
3 tsp olive oil, divided
Salt and freshly ground black pepper
1/2 cup chopped yellow onion
2 cloves garlic, minced
4 small sprigs rosemary
Preheat oven to 375 degrees. In a mixing bowl whisk together coarse mustard, dijon mustard, yellow mustard, honey and 2 tsp olive oil. Spray a large baking dish with non-stick cooking spray (large enough to fit chicken without over crowding).
In a small skillet, heat remaining 1 tsp olive oil over medium heat. Add onion and saute 3 minutes then add garlic and saute 30 seconds longer. Pour into prepared baking dish and spread into an even layer. Season each chicken breast with salt and pepper on both sides, then set chicken over onion layer in baking dish.
Pour mustard mixture evenly over chicken, working to cover each chicken breast entirely. Lay sprigs of rosemary between chicken breasts, then cover dish with foil. Bake in preheated oven 20 minutes then uncover and bake until chicken has cooked through, about 15 – 25 minutes longer (note that cook time will vary based on thickness of chicken breasts so just keep an eye on it. It should register 165 degrees in thickest part of breast on an instant read thermometer. It could be less or more time than that listed). Serve warm, spoon more sauce over chicken as desired.