Preheat oven to 400°F
Heat 2 quarts of water in a large pot over high heat until boiling. Add 2 tablespoons kosher salt, baking soda, and potatoes. Stir.
Return to a boil, reduce to a simmer, and cook until fork-tender, about 10 minutes after returning to a boil.
Meanwhile, combine olive oil or bacon fat with rosemary, garlic, and a few grinds of black pepper in a small saucepan and heat over medium heat. Cook, stirring constantly until garlic just begins to turn golden, about 3 minutes. Remove from heat.
When potatoes are cooked, drain, and allow them to rest in the strainer for about 30 seconds to allow excess moisture to evaporate.
Transfer potatoes to a bowl with infused oil, add thyme, flour, Parmesan, and season to taste with a little more salt and pepper. Toss to coat. You want a thick layer of oil, herb, flour, and Parmesan to coat the potatoes.
Transfer potatoes to a large rimmed baking sheet or skillet. Spread them out evenly and smash flat with a potato masher or bottom of a glass. Transfer to oven and roast, without moving, for 15 minutes. Using a thin, flexible metal spatula to release any stuck potatoes, turn potatoes. Continue roasting until potatoes are deep brown and crisp all over, turning and shaking them a few times during cooking, 15 to 20 minutes longer.