Heat the oven to 425°F. Cover whole baby potatoes with cold water by 1 inch, add cooking salt and simmer for 15 to 20 minutes until fully tender; drain and let steam escape for 5 minutes.
Brush a large metal rimmed sheet with 1 tablespoon oil. Make 18 small flat piles of finely grated Parmesan, spaced so the potatoes will not touch.
Flatten each warm potato gently to about 1/2 inch thick on a plate with the bottom of a glass, then set one over each Parmesan pile. Keep the skins attached where possible.
Brush tops with remaining oil and season with garlic powder, seasoning salt and pepper. Roast for 25 to 30 minutes until tops are golden and the cheese underneath is deeply browned.
Rest on the pan for 5 minutes, then slide a thin metal spatula under each cheese crust and lift carefully. Serve about 3 potatoes per person.