Place the chicken fillets on a chopping board. Using a sharp knife, slice the first fillet in half horizontally, starting from the straighter side. Don’t cut all the way through; leave the edge, allowing you to open up the fillet like a book. Repeat with the second fillet. Take two pieces of cling film three times bigger than each fillet. Lay one on the board, place the open fillet on top and cover with the second piece of film.