How to Make It
In a small jar, combine the white wine vinegar with the dried oregano. Cover and let stand at room temperature for 2 days. Strain the oregano-infused vinegar into a small bowl and stir in the olive oil.
Using kitchen shears, remove the wing tips and the backbones from the chickens. Set the chickens on a large rimmed baking sheet, skin side up, and press down firmly on the breastbones to flatten them so that the legs face the breasts. Score each breast, drumstick, thigh and wing halfway to the bone in two places per part. Drizzle all but 2 tablespoons of the vinegar-oil mixture over both sides of the chickens and rub the mixture into the meat. Cover and refrigerate for 1 hour.
In a small bowl, combine the dried sage with the kosher salt, piment d' Espelette, dried rosemary and ground black pepper. Rub the seasoning all over the chickens. Let the seasoned chickens stand at room temperature for 30 minutes.
Preheat the oven to 425°. Roast the chickens in the upper third of the oven, skin side up, basting both chickens with the remaining vinegar-oil mixture half way through, until the chicken is just cooked, and an instant-read thermometer inserted into the thickest part of the thigh registers 165°, about 45 minutes.
Preheat the broiler. Pour the pan juices into a small saucepan. Broil the chickens about 4 inches from the heat, rotating the pan, until browned and crisp, about 3 minutes. Carve the chickens. Reheat the pan juices and serve with the chicken.