Preheat oven to 400°F. Line a large baking sheet with parchment paper (not foil) to keep the cheese from sticking. Spread 1½ cups freshly shredded Parmesan into a tight rectangle on the parchment.
Peel and slice carrots into 3 to 3½-inch lengths. For thicker carrots, cut them in half lengthwise and again crosswise so each piece is about ½ inch thick. Uniform pieces help them cook evenly. If you leave the carrots too thick they won't soften as easily.
In a large bowl, whisk together olive oil, garlic, salt, onion powder, rosemary, and black pepper. Add the sliced carrots and toss well until they’re fully coated.
Place the carrots cut side down on top of the cheese layer. This helps the bottom caramelize and the cheese crisp. Rearrange as needed to fit all pieces closely together. Sprinkle the remaining ½ cup shredded Parmesan evenly over the top.
Bake for 30–35 minutes, or until the carrots are tender in the center and the cheese around the edges turns golden and crisp. For a softer texture, leave them in for an extra 5 minutes.
Let the carrots rest on the pan for a couple of minutes before removing so the cheese crust can firm up. Transfer to a serving platter and top with fresh chopped parsley if desired.