In a small bowl, combine the mustards, honey, and 2 teaspoons of the olive oil.
In a sauté pan or cast iron skillet, add 1 teaspoon of olive oil. Add the onion and sauté over medium heat until golden and tender, about 5 minutes. Add the garlic and sauté for an additional 1 - 2 minutes, until fragrant.
Transfer the onion and garlic to an oven safe dish and add the chicken to it. Salt and pepper the tops of the chicken according to your personal preference.
Pour the honey mustard mixture on top of the chicken. Arrange the rosemary sprigs around the chicken in the pan.
Bake the chicken covered at 350 degrees F for 20 minutes. Then remove the cover, baste the chicken with the sauce, and continue to cook for an additional 10 - 15 minutes uncovered, or until the chicken is browned on top and cooked through.