Dampen the baked-on food stains with water. Sprinkle salt onto the area, and allow it to sit for 10 minutes.
Rinse the salt from the cookie sheet. Wash the cookie sheet to remove loose food and residue. Wash the cookie sheet in 1 qt. of warm water with 2 tbsp. of liquid dish soap.
Scrape off food debris with a plastic scraper while the sheet remains wet. Avoid using metal scrapers because they will scratch the sheet.
Sprinkle baking soda over the baked-on food. Pour vinegar over the baking soda so that it foams. Scrub the cookie sheet with a non-abrasive sponge.
Rinse the cookie sheet with clean water. Repeat the process until you remove the baked-on food.
Allow the cookie sheet to air dry. Store the cookie sheet away from other bakeware to prevent accidentally scratching the surface.