Rosti is/are(?) shaped into a cake, and served (for breakfast, at least) as the main event--hash browns are potato slices, cubes, or shreds, cooked loose on the griddle, served as a side dish--

WLD--You can tell that they are done by the way they look--shredded potatoes are opaque when done--also golden brown in spots. The trick is really in getting and keeping the griddle, grill, or frying pan hot enough--