Peel and cut the potatoes in half or quarters (if they are large).
Wash the potatoes and add them to a large saucepan. Add enough water to cover the potatoes. Add the salt and baking soda. Bring to a boil, then reduce heat to a slow simmer and cook for 10-15 minutes. (Potatoes are ready when, you can easily pierce the potato with a fork.) Drain and let sit for a minute while the moisture evaporates.
Preheat the oven to 220°C/430℉.
Combine olive oil, garlic, rosemary (or thyme), and black peppercorns in a small saucepan and heat over medium heat. Stir constantly until the garlic begins to brown, about 2-3 minutes.
Immediately pass the oil through a fine sieve over the potatoes. Add salt and pepper to taste, stir gently to coat.
Shake gently the saucepan with potatoes so they hit all sides of the pot. This will loosen the outer layer of the potatoes and form a rough surface around each piece of potato.
Transfer the potatoes to a large baking dish, spreading them out evenly. Transfer to the oven and bake, without stirring, for 30-40 minutes.
Remove from the oven, and using a spatula or fork, flip the potatoes. Return to the oven and roast continue to roast them until the potatoes are nicely browned and crispy, another 30 to 40 minutes more.
Transfer the potatoes to a large bowl and sprinkle them with the remaining garlic-rosemary mixture (optional) and chopped parsley. Mix well and season with more salt and pepper to taste. Serve immediately.