The potatoes won't have nearly enough time to cook on their own - to get them ready, we cooked the small tots whole in plenty of salted water. The timing will depend on just how large the potatoes you use are - you want them to be tender, yet not so much that they would fall apart. When testing to see if they are ready, a sharp knife should barely give you any resistance. Since the potatoes need to be sliced, it is best to let them cool down first - not only will your fingers thank you, they are more apt to slice cleanly.
We left the skin on for the boost in nutrition, but you can certainly peel or rub them clean if you like. To take some of the bite out of the onion, the thin slices are softened in a liberal slick of extra-virgin olive oil. Three tablespoons may seem excessive for two small onions'? worth, but once they have done their business, all of those potatoes that had been thinly sliced are slid into the skillet and the oil gives them a chance to crisp and brown.
Generously seasoning the potatoes and onion with salt and fresh ground black pepper ready the skillet for the mass of beaten eggs and sharp white cheddar that were about to be poured in. I tend to mix whole eggs with egg whites to level the playing field, but I do prefer the texture where the ratio favors whole eggs. With two egg whites replacing one whole egg, we went with four extra whites and dropping the whole eggs to eight. You could probably narrow the whole egg amount to around 5 or so, but we've found the texture starts to suffer once you pass the half and half point.
As soon as the eggs were added, scant spoonfuls of sour cream were dropped all over the top and swirled in using the tip of a table knife. You could probably just whisk this right into the eggs, but what fun is that? This way you experience the tangy contrast more in the creamy puddles! With the amount of eggs, it wouldn't work so well to try and cook this through on a burner - as soon as the edge begins to set, the skillet is transferred to the oven to gently finish cooking the eggs through.
Served whole, inverted on a platter for the bonus visual bang of seeing the sliced potatoes and onions scattered around the top, let this rest for at least a few minutes to let the eggs relax before taking out wedges. I'm sure this would be a commanding dish for a hearty breakfast or brunch, but as we found out when we prepared this, the frittata also makes for a substantial meat-free dinner as well!