While I was a student at Clemson's center for architectural studies in Genoa more than forty years ago, Ilda, our lovely cook, used to make us something she called an "omeletta." It was really not an omelette in the French sense, nor was it a frittata, but something halfway between.
She put together a basic batter of beaten egg, grated cheese (both Parmigiano and mozzarella), and seasonings. After getting a carbon steel omelette pan nice and hot, she'd stir another element such as sautéed mushrooms, onions, ham, or cooked and grated potato into that basic batter. She'd then swirl a little oil or butter into the pan and pour in a ladleful of batter, all the while swirling the pan to evenly cover its bottom.
The pan was so hot that the bottom of the omeletta was almost immediately golden brown and in mere seconds it was done. She'd fold it in half, flip it onto a tray, and repeat the operation until all the batter was cooked. I've not seen anything quite like it since, but every time I make a frittata, while the technique is very different, I think fondly of Ilda's omelettas. And though a proper frittata is barely allowed to color, I still prefer mine to be a light golden brown.
My favorite of those omelettas was the one with grated potato, which was the inspiration for what has become our house favorite frittata—with ham, onions, and diced cooked potato.
Ham, Onion, and Potato Frittata
1 medium waxy white or gold fleshed potato, peeled and cut into very small dice
1 small or ½ large onion, trimmed, split lengthwise, peeled, and thinly sliced
1½ tablespoons unsalted butter or 1 tablespoon butter and ½ tablespoon olive oil
4 large eggs, at room temperature (see notes)
½ cup thinly sliced and then chopped cooked country ham or prosciutto
½ cup coarsely grated Gruyere Cheese
2 tablespoons finely grated Parmigiano-Reggiano
Whole black pepper in a mill
1. Position a rack 6-8 inches below the heat source and preheat the broiler for 15 minutes. Meanwhile, put the potato in a small saucepan or lidded skillet, cover it completely with water, and add a large pinch of salt. Bring it to a boil over medium-high heat, adjust the heat to a lively simmer, and cook until the potato is barely tender, about 4 minutes. Drain and let cool.
2. Put the onion and ½-tablespoon of butter or oil in an 8-9-inch nonstick or well-seasoned iron skillet. Put the pan over medium heat and sauté, stirring often, until the onion is softened and lightly caramelized, about 5-6 minutes. Meanwhile, one at a time break the eggs first into a small bowl and transfer each to a medium (1½-2-quart) mixing bowl. Lightly beat them until they're smoothly mixed.
3. When the onion is ready, remove the pan from the heat and scrape the onion into the eggs. Stir well and mix in the ham, cooled potato, and both cheeses. Season lightly with salt and a few liberal grindings of pepper and mix well.
4. Return the pan in which the onion cooked to medium heat and add the remaining tablespoon of butter. When the butter is melted and foaming, swirl the pan to coat it with the fat, then stir the egg mixture and pour it into the pan, carefully spreading the solid ingredients to distribute them without touching the bottom of the pan. Adjust the heat to medium low and cook until the bottom of the frittata is set and its edges are opaque to about half an inch in.
5. Transfer the pan to the rack under the broiler and broil until the frittata is set and, if you want it so, browned to your liking. Remove it from the oven and carefully slide the frittata from the pan onto a cutting board. Cut it into halves or quarters and serve hot, warm, or at room temperature. Frittate can be made up to 4 hours ahead if you are serving them at room temperature. They're best not refrigerated.