Set the glass pan on a heat-safe surface to cool completely. Do not place a hot glass pan in a sink, where sudden exposure to cold water could shatter the glass.
Pour distilled vinegar into the pan until the burned-on food is covered. Let it soak overnight. Vinegar is a weak acid that gradually dissolves the crusty food, making it easier to remove.
Add baking soda to the vinegar after an overnight soak, until the mixture begins to bubble. Wait for the chemical reaction to stop.
Remove the stuck-on food with a scrubber sponge under cold, running water. Repeat the vinegar soak if necessary until the food is gone.