Ask Mary

Because the amount of salt in salted butter can vary among brands from 1/4 teaspoon to 1/2 teaspoon per stick, many cooks prefer to use unsalted butter to control the amount of salt in a recipe.  This can be important in baking, when delicate flavors such as vanilla, can be easily masked by too much salt.  In addition, people who follow very low sodium diets for medical reasons may choose to use unsalted butter.