Always start with a clean skillet. For stubborn stuck-on food, a paste of coarse kosher salt and water can be used as a gentle scrub.
Dry the skillet completely. Wipe it dry with a kitchen towel, then heat it over medium heat on the stovetop until all the moisture evaporates.
Pour one teaspoon of oil into the skillet and rub thoroughly all over with a folded paper towel. Carefully flip the pan over, add one teaspoon of oil on the underside and repeat the process, rubbing all over, including the handle. Continue buffing until the oiled pan no longer appears greasy.
Preheat the oven to 450 F. Arrange a baking sheet on the center rack to catch any drips of oil that might come off. Place the skillet upside down and bake for 45 minutes to one hour.
Turn off the oven and let the entire pan cool to room temperature. You can take the pan out if you need to or leave it to sit and cool inside the oven.