Fill a medium-sized pot with water. Add the potatoes and 1 teaspoon of salt, then bring it to a boil.
Boil the potatoes for 10 minutes or until tender enough for a fork to easily pierce them. Drain the potatoes and place into a large bowl to cool for 30 minutes.
Oil the Blackstone with vegetable oil or cooking spray and preheat to medium-high heat.
Drizzle the olive oil and butter on top of the potatoes then toss to coat.
Place the potatoes onto the griddle, leaving at least 3 inches of space between each one.
Use the bottom of a mason jar, measuring cup, or spatula to smash the potatoes to about ¼” thickness.
Sprinkle the potatoes with lightly remaining salt, pepper, and garlic powder. Continue cooking until the bottom of the potatoes are golden brown, about 5 minutes.
Flip the potatoes and continue cooking until the other side is golden brown, about 3 additional minutes.
When done, the potatoes will be tender and browned. Top with parmesan and parsley. Serve warm.