Step 1 Preheat oven to 175 °C/ 350 °F (conventional), or 155 °C/ 310 °F (fan assisted). Place a piece of parchment paper under the chicken, and then butterfly the chicken breast so that it lays open like a book. Place a piece of plastic wrap or parchment paper over the top and flatten with a meat mallet or heavy bottomed pan. The chicken should be about 6 mm/ 1/4 inch thick.