1. Bring the chicken stock to a boil over high heat in a saucepan just large enough to hold the chicken breasts in one layer; add the chicken breasts, making sure they are covered by the chicken stock. Simmer them very gently, uncovered, for 7 minutes. Remove the pan from the heat, cover it, and let it stand for 10 minutes.

2. Remove 1 chicken breast to a plate and cut into the center to make sure the breast is cooked through. If it is, remove the remaining breasts to the plate. If it is not, return it to the saucepan, cover the pan, and simmer it for 2 minutes more, then remove the chicken to the plate and set it aside to cool. Reserve the chicken stock for another use. After the chicken has cooled slightly, use it as directed in a recipe.