Some good recipes for crispy sweet potato are Crispy Baked Sweet Potato Fries from the Foodie with Family website, and Chocolate Covered Katie's Crispy Sweet Potato Fries. The Food Network also offers a good recipe that calls for sweet potatoes, olive oil, paprika and a house seasoning.
For the Food Network's recipe, first make the house seasoning by combining 1 cup of salt, 1/4 cup of black pepper and 1/4 cup of garlic powder. Next, cut 5 sweet potatoes into long, thin pieces, and drizzle them with olive oil. Toss the potato fries with 1/2 teaspoon of paprika and house seasoning to taste, and arrange them in a parchment paper-lined tray in a single layer. Bake the fries at 450 degrees Fahrenheit for 20 minutes, and serve.
To make the Foodie with Family recipe, peel 2 large sweet potatoes. Slice them into thin strips, no bigger than 1/4 inch for the depth and thickness, and cover them in cold water for at least one hour. While the fries drain in a colander, cover two baking pans with greased foil. Place 4 teaspoons of brown rice starch in a bag, and add the sweet potato matchsticks.
After coating the fries in the starch, mix in 1/2 teaspoon of chipotle powder and 2 tablespoons of grapeseed or peanut oil, and arrange the fries on the prepared trays. Bake the fries at 425 F for 15 minutes, flip them and bake them for another 15 minutes. Allow the fries to sit in the oven with the heat off and the door open for another 10 minutes, before adding salt and serving them.