Step 1: Preheat your oven to 450°F (230°C). Place the potato chunks in a large pot and cover with cold water by at least an inch.
Step 2: Add the salt and baking soda to the water. Bring to a boil over high heat, then reduce to a simmer. Cook for about 10 minutes until the potato surfaces are tender but the centers are still firm.
Step 3: Drain the potatoes and let them sit in the colander for 2 minutes to allow excess moisture to evaporate.
Step 4: Transfer the potatoes back to the pot. Add the oil (or fat), garlic, rosemary, and pepper. Close the lid and shake the pot vigorously until the potatoes are coated in a thick layer of starchy paste.
Step 5: Spread the potatoes onto a large rimmed baking sheet in a single layer. Roast for 20 minutes, then flip each potato. Continue roasting for another 20-30 minutes, flipping occasionally, until deep golden brown and the ultimate crispy roasted potatoes are achieved.
Step 6: Remove from the oven, season with a little more salt if desired, and serve immediately.