1. Place red-pepper flakes in a spice grinder; pulse until ground. Season chicken with salt and pepper; sprinkle ground red-pepper flakes on flesh side of chicken only. Tear marjoram sprigs and 4 thyme sprigs; sprinkle evenly over both sides of chicken. Place in a large baking dish, cover, and refrigerate overnight.

2. Preheat oven to 425 degrees.

3. Heat a large cast-iron skillet over high heat; add olive oil. Remove marjoram and thyme from chicken. When olive oil is hot, add chicken, skin-side down. Place an aluminum foil-wrapped brick on top of chicken and transfer to oven. Cook until juices from chicken run clear, 8 to 10 minutes; turn and cook for 30 seconds more.

4. Transfer chicken to a large plate and set aside. Drain fat from skillet and return to medium-high heat. Add tomato paste and cook, stirring, scraping up any browned bits in pan, about 1 minute. Remove 1/2 cup of pickling liquid from peppers and add to skillet, along with chicken stock, 6 pickled peppers, and remaining 2 sprigs thyme. Let cook until sauce is reduced by half, 3 to 5 minutes.

5. Transfer sauce to a large serving platter; top with chicken; serve.