Preheat the oven to ~450-500, throw the pans in for five minutes to drive out any moisture.

Pull the pans out, and apply a very thin coat of oil using a paper towel or lint-free cloth. Flax oil is best, low-temperature oils in general are better than frying oils here. Put the coated pans back in the oven for ~45-60 minutes, then remove. Repeated coats will significantly increase the strength of the coating