Preheat and Prepare Oven: Set your oven to 400°F (200°C). Position a rack in the center of the oven. Line a baking sheet with parchment paper to prevent sticking and ease cleanup.
Mix the Flavor Base: In a large mixing bowl, combine olive oil, minced garlic, kosher salt, freshly ground black pepper, and cayenne pepper if using. Stir these ingredients well until evenly blended. Add the chopped parsley to the mixture and give it a quick toss.
Prepare and Coat Potatoes: Slice each baby potato in half. As you cut, immediately add the potato halves into the bowl with the oil and spice mixture to prevent discoloration. Toss gently but thoroughly, ensuring each piece is evenly coated with the garlicky oil and seasoning.
Add Parmesan Cheese: Sprinkle the finely grated Parmesan cheese over the coated potatoes. Toss lightly just enough to distribute the cheese without clumping, so it adheres evenly to each potato half.
Arrange for Roasting: Spread the potatoes in a single layer on the prepared baking sheet, placing them cut-side down. If any Parmesan remains in the bowl, spoon it onto the flat surfaces of the potatoes for extra crispiness. It’s fine if the potatoes are close but avoid stacking.
Roast Until Golden and Tender: Place the baking sheet in the oven and roast for 25 to 35 minutes. About halfway through, rotate the pan to promote even browning. The potatoes are ready when tender to a fork and the Parmesan has turned a deep golden brown.
Rest and Serve: Remove the tray from the oven and allow the potatoes to rest for 5 minutes. This resting step lets the cheese cool slightly, firming up its crisp texture. Using a thin spatula, flip the potatoes to reveal their crispy, cheesy sides. Garnish with additional chopped parsley and serve immediately.