Preheat an oven. Pour neutral oil in a large baking dish, then place in the oven to preheat. Place peeled, cubed potatoes in a large pot, then cover with cold water. Add Kosher salt, then bring to a boil. Cook.
Drain the potatoes over a colander, then return to the pot. Allow them to steam, then place the lid on top, carefully hold it in place, and shake the pot vigorously.
Remove the baking dish with hot oil from the oven, then carefully pour in the potatoes. Season with Kosher salt and black pepper, then toss to evenly coat in the hot oil. Ensure that the potatoes are in a single flat layer, then return to the oven. Cook.
Place chopped garlic, chopped rosemary, and extra virgin olive oil in a small bowl, then stir to combine. Set aside.
Remove the potatoes from the oven, then drizzle the garlic rosemary oil on top. Toss to evenly coat. Transfer to a serving bowl, then finish with a generous pinch of flaky sea salt. Enjoy hot!