Heat a large oven-proof skillet over medium-high heat. Add the olive oil. Season the chicken thighs with half of the salt and pepper and place in the skillet skin side down. Cook the chicken for five minutes or until the skin is golden brown. Turn the pieces over and cook for an additional four minutes.
Remove the pan from the heat, arrange the cauliflower around the chicken. Spoon the pan juices over the cauliflower. Season lightly with the remaining salt and pepper. Put the skillet in the oven and cook for about 20 minutes, or until the chicken is done and the cauliflower is crisp-tender. (Poultry is done when it measures 165 degrees F on an instant-read meat thermometer.)
Remove the pan from the oven and add the sherry vinegar. Mix it with the pan juices and spoon over the cauliflower. Add the capers. Top with parsley if desired, and serve immediately.
To cut the cauliflower into florets, try this tip from Ina Garten and cut the core out first. Then, use the tip of your knife to break away about a third of the head, and from there, cut it into florets. Once it's cut up, rinse the florets in a colander and let drain before adding them to the skillet. Leftovers can be stored covered in the refrigerator for up to four days. You can reheat them in the oven or the microwave. If you are microwaving them, place them on a microwave-safe plate, sprinkle a few drops of water over them, and microwave for a minute or so.I use kosher salt; if you are using table salt, only use one-half as much as the recipe calls for. I like to use either my large eleven-inch cast-iron skillet or a large non-stick oven-proof skillet for this recipe. To see if your thighs are done, insert your meat thermometer into the thighs' thickest part, not touching the bone. They are done when it registers 165 degrees F. If you don't have a meat thermometer, please consider getting one. They are inexpensive and a game-changer when cooking meat. If you don't have a thermometer, pierce the chicken with a fork, the juices should be clear and not pink. I usually place a splatter guard or splatter screen over the skillet when pan-searing the chicken. It keeps the splatter down and the top of my stove cleaner.