Cleaning burned baking sheet

Spread a thin layer of liquid automatic dishwashing soap (I use Cascade) over the pan. Leave overnight, scrub off in the morning. Sometimes it takes a second go at it, but this usually works the first time.

I use this method and it works every time.
http://www.savvysugar.com/Metal-Pot-Pan-Cleaner-30837082

I bet it's garbage bag. Her auto-correct was working overtime!

Adianne, what is a "carnage bag?"

If it is really baked on hard this will work but be careful because of the fumes. Place in a carnage bag. Pour 1/2 c ammonia into the bag and seal it tightly for 24 hours. Cut open the bag carefully (outside is best, but in the stationary tons with windows open will work too. Simply rinse and throw away bag. The Antonia fumes soften the crust up. It is remarkable. I do this for my oven racks when they are really grimly.

Shuna's advice is perfect. A stainless scrubber is a cook's best friend.

Thanks! Great tips! (I normally parchment, but was in a rush, threw iin some whole sweet potatoes and apples to bake off, and ended up with a much larger mess than I'd anticipated.) I never thought of using my cast iron skillet for this, but may try it out!

I would stay away from Bar Keepers friend when it comes to pans one eats off of.
To clean badly burnt pans I:
boil water, pour over, & soak pan in boiling water.
scrub with metal (non soaped) scrubby
if spots still don't come off: fine sandpaper or metal scrubby & kosher salt.
& for a last resort: place pan over burners and boil spots off.

for the future: lay down parchment paper or aluminum foil or a silpat so cleaning on the other end is not an issue. I now cook my sweet potatoes in an enamel cast iron frying pan because they are naturally non stick... best of luck!