In a large pot, bring 2 quarts (2L) water to a boil over high heat. Add potatoes, baking soda, and 1 tablespoon salt and stir to combine. Return to a boil, then reduce to a simmer over medium-low. Simmer, adjusting heat as needed, until a knife meets little resistance when inserted into a potato chunk, 8 to 10 minutes.

Meanwhile, in a small saucepan, cook garlic, oil or other fat, rosemary or thyme, and ¼ teaspoon pepper over medium heat, stirring and shaking pan constantly, until garlic just begins to turn golden, about 3 minutes. Immediately strain oil through a fine mesh strainer set over a large bowl. Reserve the strained garlic and herb solids for later.

When potatoes are cooked; drain well. Place back into the pot and let rest off heat for about 30 seconds to allow excess moisture to evaporate. Transfer potatoes to the bowl with the reserved infused oil. Add remaining 1 ¼ teaspoons salt and ¼ teaspoon pepper and toss while shaking bowl roughly, until a thick layer of mashed potato–like paste has built up on potato chunks and seasoning is evenly distributed, 15 to 20 seconds.

Set air fryer to 400°F (205℃) and preheat for 10 minutes. Add potatoes to basket in even layer, and cook until potatoes are golden brown and crisp all over, removing and shaking the basket a few times during cooking, 20 to 25 minutes.

Transfer potatoes to a large bowl and add parsley and reserved garlic-herb mixture. Toss to coat and season with additional salt and pepper to taste. Serve immediately.