1 3/4 lb white, redskin or Yukon Gold potatoes, scrubbed and cut into 1/8-inch-thick slices 1 large yellow onion, chopped 3 tbsp olive oil, divided 3 large eggs 1 cup egg whites (8 large egg whites) 1 tsp fine sea salt

Preheat oven to 400.
In a large bowl, toss potatoes, onion and 2 tbsp oil. Divide among 2 large, rimmed baking sheets, spreading in an even layer. Bake, tossing mixture and switching oven rack positions halfway, until browned, about 30 minutes; wipe out bowl.
In a bowl, whisk eggs, egg whites and salt. Add potato mixture and toss gently to coat.
In a large 12-inch nonstick skillet, heat remaining 1 tbsp oil on medium-high until hot. Add potato mixture, spreading evenly, and cook for 1 minute. Reduce heat to low and cook until eggs are set along edges but soft in center of mixture, 8 to 10 minutes. (NOTE: Mixture should hold together and slide freely in skillet when shaken; if not, loosen edges with a spatula.)
Arrange a large plate or baking sheet upside down over top of skillet and flip skillet to transfer mxiture to plate. Slide mixture back into skillet, browned side up. Cook until a toothpick comes out clean when inserted in center, 5 to 6 minutes. Remove from skillet and let cool for 10 minutes before slicing into wedges.