Begin by placing the small potatoes in a large pot and covering them with cold water. Add 2 teaspoons of salt to the water. Bring the pot to a boil over medium-high heat. Once boiling, reduce the heat to a simmer and cook the potatoes for about 15-20 minutes, or until they are fork-tender.
While the potatoes are boiling, preheat your oven to 450°F (232°C). This high temperature will help achieve that perfect crispy texture on the outside of the smashed potatoes.
Once the potatoes are cooked, drain them in a colander and let them sit for a few minutes to cool slightly. You want them warm but manageable.
On a baking sheet lined with parchment paper, place the drained potatoes. Using the bottom of a fork or a potato masher, gently press down on each potato until it is flattened but still intact. Aim for a thickness of about 1/2 inch.
Drizzle the smashed potatoes with 1 tablespoon of olive oil. Then, sprinkle the tops with garlic salt and freshly cracked black pepper.
Transfer the baking sheet to the preheated oven and roast the smashed potatoes for 20-25 minutes, or until they are golden brown and crispy. Keep an eye on them to avoid burning.
After roasting, remove the baking sheet from the oven and sprinkle the grated Parmesan cheese generously over the hot potatoes. Return them to the oven for an additional 5 minutes, or until the cheese is melted and bubbly.
Once the cheese has melted, take the potatoes out of the oven and garnish with finely chopped parsley. Serve immediately while they are hot and crispy!