Preheat oven to 450-500℉ (230-260℃).
On medium heat, heat your cast iron skillet on the stovetop.
Once hot, add 2 tbsp of oil and let it heat up for a minute or two.
Using a paper towel and a pair of kitchen tongs, spread the oil in a very thin layer all over the surface of the cast iron pan.
Place the pan upside down in your oven. Bake for 1 hour.
Once 1 hour is up, turn off the oven and leave the pan in the oven until completely cool.