Traditional Cuban flavors combine in a citrusy, garlic marinade for this easy spatchcock chicken. Use a cast-iron skillet to get the deep golden crust on the chicken and ensure even cooking.
Zest one of the sour oranges and transfer the zest to a bowl. Cut the oranges into quarters and juice them over a glass measuring cup. Juice the lemon and lime over the measuring cup until you have about 3/4 cup of citrus juice. Set aside.
In a small bowl, combine the garlic, kosher salt, pepper, cumin, oregano and red pepper flakes. Add the sour orange juice mixture and whisk to combine. Stir in the chopped cilantro and olive oil.
SPATCHCOCK THE CHICKEN:
Flip the chicken onto the breast side so that the backbone is exposed. Use a pair of poultry sheers to cut out the back bone, going up either side of the spine of the chicken (not down the spine itself.) Save the back bone for stock.
Flip the chicken over so that the breast side is facing up. Use the flat palm of your hand to press firmly on the chicken's breast until it breaks and you're able to flatten out the bird.
MARINATE THE CHICKEN:
Pour about half of the marinade into a glass baking dish. Place the chicken into the dish and make sure the inside of the chicken is in contact with the marinade. Arrange the chicken with breast side up and pour the remaining marinade over the bird. Rub the bird with the marinade to coat. Cover with plastic wrap and refrigerate 12 hours or overnight, flipping the chicken once or twice during the marinating time.
COOK THE CHICKEN:
Remove the chicken from the refrigerator about an hour before you're cooking it, so that it comes to room temperature.
Preheat the oven to 450°. Place a 10" cast iron skillet in the oven to heat.
Remove the chicken from the marinade and pat dry with paper towels. When the oven and pan are hot, use a pair of pot holders to CAREFULLY lift the pan and move it to the stove top. Place the chicken, breast side down into the pan and return to the oven. Roast for 20 minutes.
After 20 minutes, flip the chicken. Add the onions and potatoes and roll them around in the rendered chicken fat to coat. Arrange the onions and potatoes in a single layer around the chicken and continue cooking for 20 minutes or until chicken is done.
Transfer the chicken to a cutting board to rest and continue to cook the potatoes and onions for an additional 10 minutes. Remove the skillet from the oven. Transfer the potatoes to a serving platter.
Place the skillet over a medium high heat. Add the vinegar and scrape up the fond from the bottom of the pan. Add the chicken broth and continue to stir and scrape the pan to loosen any bits from the bottom. Stir in the chopped cilantro and transfer the jus to a bowl for serving.
Carve the chicken and transfer to the serving platter with potatoes. Sprinkle with additional cilantro for garnish and serve with jus.