Wash the cast-iron cookware with warm soapy water and a stiff brush. Rinse and dry it thoroughly with a towel.
Melt approximately 1 tbsp. of vegetable shortening or use 1 tbsp. of cooking oil. Apply it with a pastry brush to coat the entire inside and outside of the cast-iron piece.
Line the bottom rack of the oven with aluminum foil to catch dripping oil or shortening.
Set the oven to 400 degrees Fahrenheit.
Place the cookware on the top rack of the oven upside down. Leave it to bake for at least one hour.
Turn the oven off after one hour and allow the cookware to cool in the oven.
Remove the cast-iron piece after it cools and store it uncovered in a dry place.