Heat the duck fat to 300 degrees F.
Run the cut potatoes under colder water to remove excess starch. This will help to make the fries extra crunchy. Be sure to thoroughly dry the potatoes before adding to the hot fat. Slowly add and let blanch for about 4 to 5 minutes, until tender. Place onto a paper towel-lined plate and set aside to cool to room temperature.
Meanwhile, turn the heat up of the fat up to 360 degrees F.
To a small bowl, add 1 cup Greek yogurt, lemon zest and juice, roasted garlic cloves and stir to combine. Season with salt and black pepper and stir.
Once the oil is heated, add the fries and cook for another 2 minutes. This will create a creamy inside and crunchy outside. With about 1 minute to go, add the rosemary and sliced garlic to the fries. Cook until everything is golden brown. Sprinkle with the Parmesan cheese.
Plate a couple spoonfuls of the Greek yogurt onto the plate. Place the fries onto the plate in a big mound. Season with sea salt.
For roasted garlic, cover in foil and roast for 45 minutes to 1 hour at 325 degrees F.