Step 1: Preheat your oven to 450°F (230°C). Place your roasting pan inside the oven to heat up while you prepare the potatoes.
Step 2: Place the potato chunks in a large pot and cover with cold water by at least an inch. Add a generous pinch of salt and the baking soda.
Step 3: Bring to a boil over high heat, then reduce to a simmer. Cook for about 10 minutes until the exterior of the potatoes is soft but the center is still firm.
Step 4: Drain the potatoes and let them sit in the colander for 2 minutes to steam dry. Transfer them back to the pot and shake vigorously to roughen up the edges until a starchy paste forms on the surface.
Step 5: Carefully remove the hot roasting pan from the oven and add the oil. Transfer the potatoes to the pan, tossing them in the hot oil. Roast for 20 minutes.
Step 6: Turn the potatoes with a spatula and continue roasting for another 20-30 minutes until deep brown and crispy. In the last 5 minutes, toss with garlic and rosemary.