Soak: Wash sweet potatoes, then cut into wedges (cut in half, then cut each half into 4 pieces, lengthwise). Places wedges in a large bowl of cold water for 30 minutes to an hour.
Shake: Drain and pat wedges dry. Place in a large plastic baggie. Add cornstarch to the bag, seal shut, and shake shake shake. Potatoes should be lightly, evenly coated in cornstarch (add more cornstarch as necessary). Add all seasonings and shake again to coat.
Roasted Garlic: Preheat oven to 450°F (232°C). Remove excess paper from the head of garlic, leaving the cloves intact. Cut just the top off of the head of garlic to expose the tops of the cloves. Place the head of garlic on a sheet of aluminum foil, then drizzle 1 Tbsp of oil into the exposed cloves. Wrap the head in foil, then throw it on the racks of your preheating oven.
Bake: Place wedges in a single layer on a parchment-lined baking sheet. Drizzle with oil. Bake for 15 minutes, flip each wedge over, then bake for another 15 minutes, or until crispy. Garlic should be roasting in the oven this whole time.
Cool: Turn off oven and slightly prop open the door. Allow fries to crisp for 10 more minutes.
Sauce: While fries crisp up, combine 6 cloves of the roasted garlic with mayonnaise and lemon juice.
Serve: Remove fries, sprinkle with flaky sea salt, and serve with roasted garlic mayo.