Boil potatoes for 15-20 minutes or until fork-tender.
Preheat oven to 425 degrees.
Once the potatoes are done, run them under cool water, strain them and then allow them to sit on a baking sheet for a few minutes to dry.
Combine melted butter and garlic in a small ramekin or bowl.
Spray a baking sheet lightly with baking spray.
Using a potato masher or the bottom of a wide flat cup or metal measuring cup, press down on each potato, splitting them open and mashing them down a bit. There is no wrong or right, keep them a little high or mash them down further. If you go crazy and press too hard, simply push it back together (like play-dough).
Season each smashed potato with salt and pepper and then brush each potato liberally with the garlic butter. Season again and sprinkle with chopped Rosemary.
Bake at 425 for 15-20 minutes or until crisped to your liking. To speed things along, you could also broil for 3-5 minutes.
Once done, you can choose to brush with additional garlic butter.
Top each potato with a 4-fingered pinch of shredded Parmesan and place back in your still warm oven just until cheese mostly melts and enjoy!
You can also choose additional toppings like crumbled bacon, sour cream, Thyme, Sriracha salt, etc.