The fresher the cheese curds, the better they'll be. If you can't find local, fresh curds, order them from Ellsworth Co-op Creamery at ellsworthcheesecurds.com, or substitute kasseri cheese cubes. Kasseri, a salty Greek cheese, comes close to imitating the texture of curds. (Cheddar will work but won't add texture like the curds.) Oven-frying the potatoes in duck fat adds a rich, meaty flavor and gives them a gorgeously crisp texture. Look for duck fat in specialty markets, or order from amazon.com.