Preheat the oven to 425 degrees. Line a baking sheet with aluminum foil or parchment paper. Drizzle with a few tablespoons of olive oil on the foil and spread around, until the whole sheet is greased.
Place potatoes in the bottom of a large pot and fill with water until the potatoes are completely submerged.
Place the pot on medium-high heat. Cook the potatoes until fork tender, but not falling apart. About 15-20 minutes (depending on size).
Once cooked, remove the pot from heat.
Using a clean, lint-free tea towel, place 3-4 potatoes on the towel, fold the towel in half, and smash the potatoes using the heel of your hand (careful, this can be hot!). Then, peel back the towel and use a spatula to transfer the potatoes to the lined and oiled baking sheet.
If you do not like this method, you can also place the potatoes on the baking sheet and smash with a fork.
Once all the potatoes are on the baking sheet, drizzle with the remaining few tablespoons of olive oil, sprinkle with salt and pepper, and mix with your hands until each potato is covered with all the ingredients.
Sprinkle all of the potatoes with the shredded parmesan.
Bake for 20-30 minutes, or until the potatoes are browning and beginning to crisp around the edges.
Due to the potatoes' heat retention, wait about 5-10 minutes before eating, then serve warm.