Preheat the oven to 400°F and set a rack in the middle. Line a rimmed baking sheet with parchment paper.

In a large bowl, mix together the olive oil, grated garlic, kosher salt, black pepper, cayenne (if using), and parsley (if using).

Cut each potato in half and add to the olive oil mixture as you slice. Toss the potatoes with the oil mixture until fully coated.

Add the grated Parmesan to the potatoes and toss gently until just coated.

Arrange the potatoes on the lined baking sheet with the cut side down and scrape any remaining Parmesan mixture onto the potatoes.

Roast the potatoes until fork-tender and golden brown, 25 to 35 minutes, rotating the pan halfway.

Remove the baking sheet from the oven and let the potatoes sit for 5 minutes to allow the Parmesan to set.

Flip the potatoes to reveal the golden brown surface and transfer to a serving platter. Top with more parsley and serve immediately.

Store leftover potatoes in an airtight container in the refrigerator for up to 4 days.

To reheat, preheat the oven to 375°F. Arrange potatoes cut side down on a lined baking sheet and reheat until hot, 5 to 10 minutes.

Alternatively, reheat in an air fryer if preferred.