Cut the potatoes into halves or quarters, as long as they are all about the same size. Place the potatoes in a large bowl and add the garlic and rosemary. Generously sprinkle with salt and oil. (The potatoes will absorb a lot of oil and salt; they will taste bland if we don't go big here.)
Lay the potatoes in a single layer on a sheet tray and roast in the oven for 15 to 20 minutes. Check the potatoes halfway through the cooking process to rearrange so the potatoes will have even cooking time and get evenly browned. The potatoes should be nice and brown and really well flavored. Transfer to a serving bowl and serve. Hot potato!