Preheat your oven to 350°F and use olive oil to season your cast iron skillet well.
Wash and peel your potatoes, then using a sharp knife or Mandoline, slice the potatoes into very thin rounds (about 1/8 inch thick).
Use a double boiler to melt your clarified butter.
Arrange a single layer of overlapping potato slices in a circular pattern, going clockwise around your cast iron skillet.
Use a basting brush to brush on some of the clarified butter. Then evenly sprinkle on the seasonings, including salt, pepper, Herbes de Provence, and the grated Pecorino Romano and Parmesan cheese blend.
Repeat the layering process, brushing with butter and adding seasoning and cheese until all your potatoes are used.
Bake uncovered for 60 - 90 minutes or until the top of the potatoes are crispy and golden brown.
When finished set your layered potato bake aside and let it cool for about 5 minutes. Once cooled, use a spatula to loosen the edges. Carefully invert the layered potato bake, and flip it out onto a flat surface like a cutting board or serving tray.
Slice the potato bake, garnish with fresh rosemary and chives if desired, and serve with a dollop of sour cream for extra flavor.