Wash the cast iron with warm water and a small amount of mild soap if needed
Scrub off any rust or residue
Dry the pan completely with a towel
Heat the oven to 450–500°F
Apply a very thin layer of cooking oil to the entire pan, inside and out
Wipe off all excess oil so only a light sheen remains
Place the pan upside down on the middle oven rack
Put a baking sheet or foil on the lower rack to catch drips
Bake for 1 hour
Turn off the oven and let the pan cool inside
Repeat the process 2–3 times for a stronger seasoning layer