How to Make It
Preheat the oven to 425°. Using poultry shears, cut along each side of the chicken backbone and remove it. Turn the chicken breast side up and press on the breastbone to flatten the chicken. (Alternatively, ask your butcher to do this for you.) Season with salt and pepper.
Heat a large ovenproof skillet over moderately high heat. Add the olive oil, then add the chicken, breast side down. Place another heavy pan or pot on top of the chicken and press down firmly. Reduce the heat to moderate and cook until the skin is browned, about 5 minutes.
Remove the top pan and turn the chicken over. Transfer the skillet to the oven and roast the chicken for 25 minutes, until an instant-read thermometer inserted in an inner thigh registers 160°. Transfer the chicken to a platter and let rest for 10 minutes.
Set the hot skillet over high heat; add the parsley, capers and garlic and cook for 30 seconds, until sizzling. Add the chicken stock and lemon juice and cook, stirring and scraping up any browned bits, until the sauce has reduced by half. Stir in the anchovies and pour the sauce over the chicken.
Arugula salad and lemon wedges.