Peel sweet potato and cut into "fries". About 1 cm wide and 1 cm thick (compare to a fingernail!). You can cut your potatoes as long or short as you prefer
Add all fries to the mixing bowl, completely covered in water, and allow to sit for at least 45 minutes
Put your sheet pan into the oven and preheat to 400 degrees F (every oven will heat up at different rates - I start heating mine up at about 30 minutes)
Add 3 tablespoons cornstarch, 1 teaspoon seasoning salt and 1 1/2 teaspoons dried rosemary to your zip bag
After 45 minutes, remove fries from bowl, letting excess water drip off and lay the fries onto paper towel. Do not pat completely dry. You want them to be a little damp for the cornstarch and seasonings to stick
Add the fries to the zip bag and give them a really good shake, coating them as much as you can (there will be some seasoning that doesn't stick - that's okay!)
Next, about 1 tablespoon at a time, add the oil, shake after every addition. You may have to massage the fries a bit to make sure they are well coated
Remove your pan from the oven and carefully place your parchment on top
Add seasoned fries to your parchment lined pan, keeping them separate from one another. Don't forget your pan is hot!
Place pan into oven and bake fries for 35 minutes, no need to turn them
Meanwhile, make your Maple Mayo by stirring 1/2 cup mayo and 1 tablespoon maple syrup together with pinches of salt and pepper
Once 35 minutes are up, turn on broil for 2-3 minutes for a little crisp up. Every oven is different so keep an eye on your fries so they don't burn.