Wash potatoes then thinly slice. Place potato pennies in a large bowl then cover with water and ice. Soak for 30 minutes.
After 30 minutes, remove potatoes from ice water and dry them thoroughly with a paper towel.
Preheat oven to 450 degrees F. Line two rimmed baking sheets with parchment paper. Set aside.
Place dried potatoes into a large zip-top plastic bag then add garlic powder, smoked paprika, salt, pepper, and olive oil. Shake well to coat.
Place coated potatoes in a single layer on parchment paper-lined baking sheets.
Bake 20-35 minutes until potatoes are cooked through and crispy.
Immediately transfer potatoes to a large bowl and add both types of parmesan cheese and parsley. Toss to coat.