Preheat the oven to 425°F. Slice a thin piece off the bottom of each potato to create a flat, stable surface.
Slice the potatoes: Place a potato, cut-side down, between two chopsticks, skewers, or wooden spoon handles. Cut thin slices crosswise, about 1/8-inch apart, stopping when your knife hits the chopsticks so you don’t slice all the way through. Repeat with the remaining potatoes.
9 medium gold potatoes
Make the Parmesan mixture: In a small bowl, stir together the Parmesan, olive oil, garlic, 1 teaspoon rosemary, 1 teaspoon thyme, onion powder, kosher salt, and black pepper.
1 cup finely grated Parmesan cheese, 2 Tablespoons olive oil, 3 cloves garlic, 2 teaspoons chopped fresh rosemary, 2 teaspoons fresh thyme leaves, 1/2 teaspoon onion powder, 1 teaspoon kosher salt, Black pepper
Arrange the potatoes: Spoon 9 evenly spaced mounds of the cheese mixture onto a light-colored, rimmed baking sheet. Spread each mound to roughly match the bottom of a potato. Place the flat side of each potato directly onto the Parmesan mixture, pressing gently so the cheese adheres to the bottom.
Make the herb butter: Melt the butter with the remaining rosemary and thyme. Set aside for brushing near the end of baking.
3 Tablespoons unsalted butter
Roast the potatoes: Roast for 25 minutes, checking the Parmesan crust toward the end to make sure it isn’t getting too dark. Carefully slide a thin spatula beneath each potato, keeping the crust attached, and use a fork to help turn it Parmesan-side up. Roast for another 15 minutes.
Brush with butter: Remove the pan from the oven and flip the potatoes cut side up again. Brush the potatoes with the melted herb butter, gently working it between the slices where accessible. Return to the oven for about 5 minutes, or until the potatoes are fork-tender in the center and the Parmesan crust is deeply golden.
Finish and serve: Brush the potatoes with the butter and oil from the pan, sprinkle with flaky salt, and serve hot.
Flaky salt