Pat the chicken thighs dry with a paper towel while you preheat the oven to 410°F. Sprinkle salt, black pepper, and the French Herb & Mustard Seasoning over each piece of chicken, and then drizzle olive oil over them and rubbing oil and seasonings into the meat.
Arrange the seasoned chicken thighs in a baking pan so that they are spread out evenly, preferably not overlapping one another. Sprinkle the garlic cloves and the (optional) Rosemary leaves in the pan.
Bake chicken in the 410° oven for 30 minutes. Reduce the heat to 375°F and bake for an additional 20 minutes, or until the chicken is tender when poked with a knife and juices run clear. Remove the baking sheet from the oven and cover pan with aluminum foil to keep chicken warm until serving time.
Adapted from GiveRecipe.