Preheat your oven to 425°F (220°C).
Scrub the potatoes clean, then cut them into halves or quarters.
In a large saucepan, add the potatoes and cover them with cold salted water.
Bring to a boil and cook for about 5 minutes until they begin to soften around the edges.
Drain and let them steam dry for a few minutes.
Heat a large roasting pan in the oven for about 5 minutes.
Add the olive oil and return it to the oven until it's smoking hot.
Carefully add the potatoes to the hot oil.
Turn them to ensure they are well-coated in oil.
Sprinkle the salt, black pepper, rosemary, and garlic over the potatoes.
Spread them out in the pan so they roast evenly.
Roast the potatoes in the oven for about 1 hour, turning them halfway through, until they are golden brown and crispy.