Alternatively, you can place the chicken in a plastic bag, as long as you ensure that there is no air in the bag, and there is enough extra space for the chicken to flatten out. Many chefs prefer moistening their wax paper or plastic wrap with water to ensure that the chicken doesn’t stick too much. [1] X Research source
If you don’t have a meat mallet, you can pound the breast with a rolling pin.
If your chicken breast is uneven or not flat enough, simply place the wax paper or plastic wrap back on it and pound out the uneven spots.
