Serve this dish with creamy polenta or couscous to sop up the chicken's delicious sweet–tart sauce.Plus: More Chicken Recipes and Tips
Preheat the oven to 400°. Heat 1/4 cup of oil in each of 2 large skillets. Season the chicken legs with salt and black pepper. Add 5 of the chicken legs to each skillet, skin side down, and cook over moderately high heat until the skin is crisp and browned, about 8 minutes. Turn and cook for 3 minutes longer. Transfer the chicken legs to 2 baking sheets or large platters, skin side up. Repeat with the remaining chicken legs. Reserve the skillets.
Add half of the onions to each skillet and cook over moderately high heat, stirring occasionally, until softened slightly, about 5 minutes. Divide the sage, bay leaves, raisins and crushed red pepper between the skillets and cook, stirring occasionally, until the onions are golden and starting to stick to the bottom of the skillet, about 5 minutes. Add 5 cups of apple cider to each skillet and simmer over moderately high heat until the cider is syrupy, about 25 minutes. Add 1/2 cup vinegar to each pan and simmer for 2 minutes. Season lightly with salt and black pepper. Stir 6 cups of stock and 1/4 cup parsley into each skillet. Season lightly with salt and black pepper.
Divide the onion-raisin sauce between 2 large roasting pans. Arrange the chicken legs in the sauce, skin side up. Set the roasting pans on the upper and lower racks of the oven and reduce the heat to 350°. Roast the chicken until cooked through, about 1 hour and 15 minutes; switching the roasting pans from top to bottom and front to back halfway through.
Transfer the chicken legs to 2 platters. Set each roasting pan over high heat and boil the sauce until the liquid in each roasting pan is reduced to about 5 cups, about 10 minutes. Season the sauce with salt and pepper and serve with the chicken.
The chicken and sauce can be refrigerated separately overnight. Bring to room temperature, then reheat the chicken in the sauce, skin side up, for 30 minutes in a 350° oven.