Place sweet potatoes directly on middle rack of the cold oven.
Place a foil-lined baking sheet on bottom oven rack.
Turn oven to 425 and set timer for 60 minutes (the oven preheating is part of the 60 minutes).
When the timer ends, do not open the oven door. Turn the oven off and leave sweet potatoes in for another 45 minutes. This step allows the meat of the potato to separate from the skin.
Remove, let cool, and enjoy!
Notes
You may end up with some residue on your oven rack. Simply wipe off with a wet rag or brush while the oven is warm.