Preheat your oven to 400°F (200°C). Line two large baking sheets with parchment paper for easy cleanup.

Using a mandoline or a very sharp knife, carefully slice the sweet potatoes into very thin, uniform rounds, about 1/16 to 1/8 inch thick. Uniformity is key here for even cooking and crispness!

In a large bowl, combine the sliced sweet potatoes, olive oil, grated Parmesan cheese, chopped fresh thyme, flaky sea salt, and freshly ground black pepper. Toss gently with your hands until every sweet potato slice is evenly coated. This generous coating is essential for developing that incredible crispy edge.

Arrange the sweet potato slices in a single layer on the prepared baking sheets. Make sure the slices do not overlap significantly. Giving them space allows the heat to circulate properly, ensuring they roast rather than steam, which is the secret to achieving that perfectly crispy edge. You may need to use both baking sheets.

Bake for 15-20 minutes, flipping the slices halfway through, until they are golden brown and crispy around the edges. Keep a close eye on them during the last few minutes, as thin slices can brown quickly.

Once baked, carefully stack the crispy sweet potato slices onto a serving platter or individual plates. Garnish with a few fresh thyme sprigs and a sprinkle of extra flaky sea salt, if desired. Serve immediately and enjoy that amazing crispy golden texture!