Peel and halve your onions, then thinly slice them about 2-3 mm thick. In a large pan, add 1 tbsp oil, and sauté your onions over medium heat for 10-15 minutes, stirring often. Season your onions with a pinch of salt. Let your onions cool down in the pan off to the side.

Peel your potatoes, and cut them in half lengthwise. Using a mandoline, slice your potatoes 3-4 mm thick. Transfer your potato slices into a large container of cold water. Change the water 3-4 times, until the water runs clear. Strain the potatoes and dry them out on paper towel.

In a large, wide pot, bring your olive oil to 350 degrees Fahrenheit. Add your potatoes into the oil a few at a time. Once the potatoes are in the oil, you want it at a temperature of 275 degrees Fahrenheit. Cook your potatoes for 5-10 minutes, stirring often, until they are a pale golden brown colour. Using a slotted spoon, remove the potatoes from the oil and transfer them to a large sheet tray lined with a wire rack. Season your potatoes with salt, and let them cool to room temperature.

In a large bowl, crack your 10 eggs. Using a spatula, stir your eggs to combine. Add your onions, and stir to combine. Lastly, add your potatoes and mix them in as well. Season everything with one last pinch of salt, and several cracks of ground black pepper. Let the bowl sit for at least 10 minutes before cooking.

When ready to cook, pre-heat an 8" or 9" non-stick pan over medium heat. Add ¼ cup of olive oil. Add your egg mix to the pan, and stir the mix for the first 10 seconds. Let the egg cook for 4-5 minutes over low heat, or until you see light brown colour developing underneath the egg when you lift it with your spatula. Using a large plate or tray, flip your omelette out of the pan, then back into the pan with the cooked side facing up. Let your egg cool for another 4-5 minutes, or until the other side also has light brown colour developing. Add more olive oil around the edge of the omelette if needed. Flip your omelette every 2 minutes or so, until the middle of the omelette registers 60 degrees Celsius with a thermometer. Remove your omelette from the pan, ideally onto a wire rack to allow it to cool evenly.