Preheat the oven to 375°F (190°C). Grease the bottom and sides of a 9-10 inch (23-25cm) cast iron pan with butter. Set aside.
Use a mandoline, or a food processor to slice potatoes very thinly.
Transfer the sliced potatoes to a large bowl.
Add olive oil, Parmesan cheese, thyme, garlic, breadcrumbs, paprika, chili flakes, cumin if used, salt and pepper.
Make sure every slice is lightly coated.
Layer the potato slices into stacks and arrange them in the prepared pan, stacked vertically.
Continue stacking until you fill the pan.
Bake uncovered for 60-70 minutes until the edges and tops are crisp and golden brown and the centers are tender. Sweet potatoes brown faster than regular potatoes, keep an eye near the end. If necessary, top with aluminum foil and continue roasting.
Let the dish rest 1–2 minutes.
Top with crumbled feta and drizzle lightly with 1–2 tsp honey if desired.
Sprinkle with fresh herbs to finish. Serve hot and enjoy!