To make the chicken, heat the oven to 180C/fan 160C/gas 4. Pull off the false fillet from each breast if it is still attached. Put the main chicken breast on a board, skinned-side down. With a small knife, make a pocket in the chicken by cutting along the length and into the side of the breast. Be careful not to cut all the way through. Mash together the cheese, garlic and rosemary and season well. Divide between each pocket, spreading evenly. Bash out the false fillets (if you have them) a little then use them seal over the cuts in the fillets.