Fill a large bowl with ice water. Peel the sweet potatoes. Cut the potatoes into french fry shapes, making sure to do very thin fries. The thinner they are, the more crispy they will stay. You are looking for between 1/4 inch and 1/2 inch. Once cut, place the fries into the ice water. Allow them to soak for about an hour.
Strain the water from the fries and dry them with paper towels. You want them as dry as possible on this step.
Preheat oven to 500.
When the oven is just about preheated, brush a little peanut oil onto a large baking sheet that will fit all the fries. Place the baking sheet into the oven to preheat for 5 minutes.
Remove the pan from the oven and add the fries to it. Add them one by one and spread them out evenly. Place the pan back into the oven and set the timer for 10 minutes.
After 10 minutes, move the fries to the top rack and turn the broiler on high. Cook another 10 or so minutes, until the fries are blackened around the edges. Remove from heat.
Serve with your favorite dipping sauce.
