Combine the vinegar, honey, brown sugar, soy sauce in a large bowl. Whisk until honey has dissolved.

Pour mixture into a large resealable plastic bag. Add rosemary sprigs and garlic cloves.

Add the chicken and seal the bag with as little air as possible in the bag. Marinate in the refrigerator for two hours.

Preheat the oven to 450 degrees F.

Place the chicken drumsticks on a greased foil-lined baking sheet. Reserve marinade.

Bake until the skin is caramelized and slightly crispy, about 30 to 35 minutes.

In the meantime, place the marinade in a small saucepan. Bring to a boil. Reduce heat to medium low and simmer for 15 minutes. This will help thicken the sauce and kill any bacteria that can cause food poisoning.

Add cornstarch, 1 teaspoon as a time, until sauce reaches desired thickness. The sauce will continue to thicken once removed from the heat.

Remove chicken from the oven. Brush on sauce. Sprinkle with sesame seeds.