Preheat the oven to 400°F (207°C). Make sure your oven is fully preheated for even cooking.
Using a mandolin slicer, thinly slice the peeled sweet potatoes. Aim for even thickness to ensure they cook uniformly. Pat the slices dry with paper towels to remove excess moisture.
Place the sliced sweet potatoes in a large bowl and add the unsalted butter, Maldon sea salt flakes, freshly ground black pepper, and chopped rosemary or oregano. Toss everything together until fully coated.
Carefully arrange the sweet potato slices upright in a small baking tray. Avoid packing them too tightly to promote crispiness.
Bake for an hour, or until the sweet potatoes are cooked through and crispy. They should be golden brown when finished.
Serve immediately for the best texture, topping with your favorite additions if desired.
