Slice 8 small Yukon gold potatoes, place in a microwave safe dish, rinse under cold water then cover with cling wrap and microwave on high for about 4 minutes. Check to see if the potatoes are tender. Drain and set aside to cool to room temperature.
Peel 1 large Spanish onion and slice into thin slices. Add 1 tablespoon of olive oil to an 8" nonstick skillet and heat over medium heat. Add onions and stir to combine. Season with kosher salt and cook until the onions are caramelized about 15 minutes. The Remove pan from heat and allow to cool for about 10 minutes.
While the onions are cooking, add 4 whole eggs to medium sized mixing bowl and whisk until completely combined. Season with kosher salt. Add the cooled potatoes and onions and stir to combine. Refrigerate for about 20 minutes and up to overnight if making ahead.
Preheat oven to 375℉
Add 1 tablespoon of oil to a medium sized skillet or 2 small skillets. Add the egg, vegetable mixture to the pan and bake for 30 minutes.Allow to cool for 10 minutes before inverting on a plate. Place a plate that is larger than the pan over the pan and invert the pan over the plate.
Serve with crisp slices of baguette and Romain and Bell Pepper Salad or dill pickles.
