Heat apple cider over medium high heat and cook for approximately 20 minutes or until reduced by half and thickened. Set aside to cool.
Preheat oven to 475 degrees F. Season chicken wit salt and pepper. Heat oil in a 12″ cast-iron or heavy nonstick skillet over high heat until hot but not smoking. Nestle chicken in skillet, skin side down, and cook 2 minutes. Reduce heat to medium high; continue cooking skin side down, occasionally rearranging chicken thighs and rotating pan to evenly distribute heat, until fat renders and skin is golden brown, about 12 minutes.
Transfer skillet to oven and cook 13 minutes. Flip chicken; continue cooking until skin crisps and meat is cooked through, about 5 minutes longer. Transfer to a plate; let rest 5 minutes before serving.
In the meantime, combine 2 Tablespoons of the apple cider (reserve remainder for another use), 2/3 cup apple jelly, Dijon mustard, apple brandy and grated ginger in a saucepot and bring to a boil. Reduce heat to medium low and let simmer for about 10-15 minutes.
Pour over chicken and serve.