Heat the olive oil in a cast-iron skillet. Add the minced shallot and the garlic. Keeping the heat low, sauté until the shallot and garlic starts to color, but make sure it does not burn.
Add the thin potato slices and sauté over low-medium heat for about 10 minutes, moving the potatoes around with a wooden spoon or spatula every now and then so they all cook evenly. The potatoes will soak up the oil and the pan will become dry: I remedy this by adding a few tablespoons of water to the pan every 2 minutes or so. You could keep adding oil instead, if you like, but water works just fine.
When the potatoes are tender, add the kale and stir around for a couple of minutes. Add the rosemary leaves and cook for another minute or two. Use a spoon or spatula to make sure the potatoes and kale are distributed evenly across the pan.
Pour in the beaten eggs and swirl the pan around so the eggs cover the potatoes and kale. Keep the heat as low as possible and cook, covered, until the bottom is golden brown and the egg at the top is set. If using the cheese, add it toward the end of cooking, so it melts.
When finished cooking, allow the frittata to cool before cutting it into slices. Depending on how much and what kind of cheese you used, if any, sprinkle with a little coarse salt before serving. You can also squirt with a little of your favorite hot sauce, if that's your thing.