In a bowl whisk together olive oil, garlic, rosemary and vinegar.
Pat the chicken dry with paper towels. Season both sides of the chicken thighs with salt and pepper. I don't measure the salt and pepper, just liberally season.
Place the chicken in a resealable plastic bag and pour the marinade over the top. Seal the bag and rub the marinade into the chicken pieces. Refrigerate for at least 3 hours.
When ready to bake, preheat oven to 350 degrees. Place chicken in a large baking dish (I used a 9x13 inch casserole) and pour any leftover marinade over the top. Bake for 30 - 35 minutes or until chicken is cooked through.
Transfer chicken to a serving platter, spoon some of the pan juices over the top garnish with a few sprigs of rosemary and serve.
Notes
Keep in mind that vinegar can impact the texture of the chicken if allowed to marinate for too long. Don't marinate for longer that 8 hours. Nutrition information for estimation purposes only.