Pour plenty of oil over the bottom of the baking dish. Spread half of the thyme sprigs on top. Scatter half of the chilli flakes and garlic on top. Place the chicken breasts on top. Sprinkle with the remaining chilli flakes and garlic. Spread the remaining thyme sprigs on the meat, press lightly and drizzle generously with oil. Cover with foil and leave to marinate in the refrigerator for at least 2-4 hours.
Then carefully turn the breasts over and let stand cold for another 2-4 hours.
Preheat the oven to 200 degrees.
Salt the chicken breasts before putting the casserole dish and its contents in the oven. Cook for about 20 minutes.