To prep the chicken:
On a work surface, place the chicken breast-side down with the neck of the chicken facing you. Using kitchen shears, cut along the length of the backbone on both sides and remove. Turn the chicken over, breast-side up. Open it on the counter and flatten the chicken as much as you can with your hands.
In a large metal bowl, whisk together the sugar, salt, and hot water, until the sugar and salt are dissolved. Add the onion, peppercorns, tarragon, garlic, ice water, and wine. Stir well. Add the chicken to the brine. Place in the refrigerator for 1 hour.
Preheat the oven to 400 degrees F.
Remove the chicken from the brine and dry well with paper towels. Set the chicken aside. Place a large skillet over medium-high heat. Add the olive oil to the hot skillet, and then place the chicken into the skillet skin-side down. Place another heavy pan on the chicken pressing it down firmly to get maximum skin contact with the hot skillet. Reduce the heat to medium and cook under the weight for 8 to 10 minutes. Once browned, remove the weights; turn the chicken skin-side up. Place the chicken in the oven until the meat is 160 degrees F, about 20 to 25 minutes. Let the chicken rest 10 minutes before serving.