Preheat your oven to 400°F (204°C).

In a mixing bowl, whisk together brown sugar, Dijon mustard, olive oil, minced garlic, salt, black pepper, thyme, and apple cider vinegar until the sugar dissolves and the mixture becomes smooth and glossy.

Place chicken thighs in a 9×13-inch baking dish or oven-safe skillet, skin side up. Pour the marinade over the chicken, using a spoon or brush to coat each piece thoroughly, making sure to get some under the skin for maximum flavor.

For deeper flavor, you can marinate in the refrigerator for up to 2 hours, but it's not necessary if you're short on time.

Bake uncovered for 25-30 minutes until the internal temperature reaches 165°F (74°C) when you insert a meat thermometer into the thickest part without touching bone. The skin should turn golden brown with dark caramelized edges.

For extra crispy skin, broil for 2-3 minutes at the end, watching carefully to prevent burning.

Remove from the oven and let rest for 5 minutes before serving. This resting period allows the juices to redistribute throughout the meat.