Adjust oven rack to center position and preheat oven to 450°F (230°C) or 400°F (200°C) if using convection. Heat 2 quarts of water in a large pot over high heat until boiling. Add 2 tablespoons kosher salt, baking soda, and potatoes; stir and return to a boil, then reduce to a simmer and cook until a knife meets little resistance when inserted, about 10 minutes.

Meanwhile, combine olive oil, duck fat, or beef fat with rosemary, garlic, and a few grinds of black pepper in a small saucepan and heat over medium heat. Cook until garlic just begins to turn golden, about 3 minutes. Immediately strain oil through a fine-mesh strainer set in a large bowl.

When potatoes are cooked, drain carefully and let them rest in the pot for about 30 seconds to allow excess moisture to evaporate. Transfer to bowl with infused oil, season to taste with more salt and pepper, and toss to coat until a thick layer has built up on the potato chunks.

Transfer potatoes to a large rimmed baking sheet and separate them out evenly. Roast for 20 minutes without moving, then using a thin spatula to release any stuck potatoes, shake pan and turn them. Continue roasting until deep brown and crisp all over, about 30 to 40 minutes longer.

Transfer potatoes to a large bowl and add garlic/rosemary mixture and minced parsley. Toss to coat and season with more salt and pepper. Serve immediately.