Hi there Alix,
Similar situations have happened to me more times than I can count. Basically, from what I've been told, the brown stain is burned sugar.
In these circumstances, I relegate the item to "Saturday/after school clothing," meaning that I wear it when it doesn't matter and every time it goes through the laundry, I scrub extra soap (I use liquid Tide) into the stain before washing. After about 15-20 washes, the stain finally goes away.
Most folks would probably opt for the "credit card to the mall" but I'm stingy...
Hope this helps!