Preheat oven to 450°F (230°C) and place a heavy-rimmed baking sheet inside.
Bring 2 quarts of water to a boil in a large pot; add baking soda, 2 tsp kosher salt, and potato chunks.
Reduce heat to a simmer and cook for 10 minutes until the exterior of the potatoes is soft but the centers are still firm.
Drain potatoes and allow to steam dry in the pot for 2 minutes.
Shake the pot vigorously to roughen the surface of the potatoes, creating a layer of starchy paste.
In a small bowl, combine oil, garlic, rosemary, sea salt, and pepper; pour over potatoes and toss to coat thoroughly.
Spread potatoes onto the preheated baking sheet in a single layer.
Roast for 20 minutes without moving them.
Flip potatoes with a thin metal spatula and continue roasting for 25 to 30 minutes until deep golden brown and crisp.
Remove from oven and serve immediately.