1/4 cup extra-virgin olive oil
8 to 10 red potatoes (2 to 3 pounds total), preferably similar in size, peeled and cut into 2- to 3-inch chunks
2 tablespoons flour
2 to 3 fresh rosemary sprigs (optional; okay to substitute dried rosemary)
3 to 4 chopped cloves garlic (optional)
Flaky sea salt, such as Maldon
Preheat oven to 400 degrees with the rack in the middle. Add the oil to a rimmed sheet pan (13-by-18-inches) and place it in the oven.
Meanwhile, bring a large pot of water to a boil. Add the potatoes and boil until softened, 4 to 5 minutes. Drain the potatoes in a colander and sprinkle with the flour. Shake the colander to distribute the flour evenly.
Carefully remove the pan with the hot oil from the oven. Spread the potatoes out in a single layer in the hot pan. The potatoes should sizzle upon making contact with the hot oil. Return the baking sheet to the oven and roast the potatoes for about 1 hour, until golden brown. Every 15 to 20 minutes, flip the potato pieces, ensuring that all sides brown evenly. About 45 minutes into cooking, sprinkle the potatoes with the rosemary and/or the garlic, if using. Transfer to a cooling rack and generously season with the salt and serve.