Pour enough vinegar in the pan to completely cover the bottom.
Add an amount of water equal to the vinegar you poured in, along with a tablespoon of baking soda.
Place the pan on the burner and let it boil for 20 minutes. This will loosen the stains on the bottom of the pan.
Turn off the heat and pour out the mixture. Put enough baking soda into the pan that it coats the bottom and scrub it out with a mesh cleaning cloth. Make sure you rinse it thoroughly before cooking with it again.