Preheat your oven to 450ºF.
Mix together Dijon mustard, maple syrup, and 1/4 tsp of rosemary, and rice vinegar. Put chicken thighs into a foil-lined, oven-roof baking dish.
Then, salt and pepper the thighs. Pour your maple mustard mixture over them, turning the thighs in the mixture so they are fully coated. Put the chicken thighs into the oven, and let them bake for 40 minutes or until a meat thermometer reads165ºF. If using bone-in thighs cook time may take another 5 minutes.
Baste the tops of the chicken with more sauce half way through. Let the chicken rest for 5 minutes before serving. Plate the chicken, making sure to spoon some extra sauce over the top. Sprinkle with fresh rosemary and enjoy.