Wash sweet potatoes well and slice them thinly on mandoline or with a sharp chef's knife. DO NOT PEEL THEM.
Sprinkle them with kosher salt (around 1/2 teaspoon coarse kosher salt) and let them sit in a colander to drain for 20-30 minutes.
Preheat the oven to 250°F. Lightly coat 2 aluminum baking sheets with olive oil. Do not use parchment paper or anything else - just the baking sheet.
Rinse your sweet potatoes under cold water and drain very well on paper towels or clean kitchen towel. Drizzle them with olive oil, making sure each chip is coated well with oil.
Spread in a single layer on your prepared baking sheets. Bake in preheated oven for 1 hour.
Turn each sweet potato chip and bake it for another 30-60 minutes (will depend on how thinly you sliced them,) until they are crisp and look like chips. In addition, rotate baking sheets from top to bottom and turn them 180° for even cooking.
Transfer to a paper towel lined plate (to remove extra oil) and season with kosher salt to taste. Feel free to add any other spices of choice (paprika, chipotle, cayenne, garlic powder, etc.)
Just to confirm, the total baking time will be around 1.5-2 hours. Enjoy!