01 - Preheat oven to 425°F. Line a baking sheet with parchment paper.
02 - Wash and scrub potatoes thoroughly, leaving skins on.
03 - Set each potato on a cutting board. Using a sharp knife, make thin slices about 1/8 inch apart across the potato, stopping just before cutting all the way through to keep the base intact.
04 - Gently fan the potato slices apart for even seasoning.
05 - In a small bowl, combine melted butter, olive oil, minced garlic, sea salt, and black pepper.
06 - Place potatoes on prepared baking sheet. Brush with half of the butter mixture, ensuring some gets between the slices.
07 - Roast potatoes for 30 minutes.
08 - Remove from oven and brush potatoes with remaining butter mixture.
09 - Return potatoes to oven and roast for 20 minutes more, or until edges are golden and crisp and interiors are tender.
10 - Remove from oven and sprinkle with parsley, thyme, and Parmesan cheese if desired. Serve immediately.