For the chicken dry rub. Combine all ingredients in a small bowl and whisk or stir until well blended.
Prepare the chicken thighs and season them. Drizzle the baking pan with olive oil. Pat and dry the chicken thighs with a paper towel. Arrange them in the greased baking pan. Spray or brush the chicken thighs with vinegar. Then generously season the chicken thighs with the dry rub, ensuring that the seasoning is evenly distributed both on the surface and beneath the skin. If short of time, you can bake after you season the chicken thighs. For the best flavour make it ahead and marinate them overnight.
To make crispy skin on the chicken thighs. Carefully lift the skin away from the chicken meat and insert two toothpicks between the skin and the meat. Using the toothpicks, the chicken skin should be tent-like to minimize steaming and promote a crispy texture during baking.
Prepare the potatoes. Wash and dry the potatoes or pat dry with a paper towel. Drizzle them with olive oil and season with salt and pepper (you may add cayenne pepper to taste if desired). Subsequently, place the potatoes in the baking pan alongside the chicken thighs. Don’t overcrowd them. Ensure at least a half inch between, so the chicken and potatoes will crisp up.
Bake the chicken thighs and potatoes in a preheated oven at 400°F for approximately 30 to 40 minutes, depending on the size of the chicken thighs. Midway through the baking process, loosely cover the dish with aluminum foil to prevent the chicken skin from becoming overly dark or burnt.
Remove the aluminum foil five minutes before completing the cooking process to enhance the crispiness of the chicken skin.
Remove from the oven and let it rest for 5 to 10 minutes in the pan. Remove the toothpicks from the chicken thighs and serve. Garnish with freshly chopped parsley if desired.