Fill a large pot with water and boil. Add salt, baking soda, and potatoes, and stir.
Return to a boil, reduce to a simmer, and cook for 10 minutes after returning to a boil. A fork should easily pierce the potato pieces by the end. Drain and let sit one minute while moisture evaporates.
Combine olive oil, rosemary (or thyme), garlic, and a few grinds of black pepper in a small saucepan and heat over medium heat. Stir constantly until garlic just begins to turn golden, about 2-3 minutes.
Immediately strain oil through a fine-mesh strainer over the potatoes. Add salt and pepper to taste, and mix.
Shake the pot that the potatoes are in so that they slam against all sides of the pot, this will loosen the outer layer of the potatoes to form a mashed layer around each potato piece.
Preheat oven to 425°F (220°C).
Transfer potatoes to a large rimmed baking sheet and separate them, spreading them out evenly.
Transfer to oven and roast, without moving, for 30-35 minutes.
Using a thin, flexible metal spatula flip potatoes. Continue roasting until potatoes are deep brown and crisp all over, turning and shaking them a few times during cooking, 30 to 40 minutes longer.
Transfer potatoes to a large bowl and add the garlic-rosemary mixture (optional) and minced parsley. Toss to coat and season with more salt and pepper to taste. Serve immediately.