Peel and halve the onions, then cut into slices

Caramelize the onions in a stainless steel pan with extra virgin olive oil on high heat initially, then reduce heat, for approximately 1-1.5 hours until sweet and deeply colored, adding water as needed to prevent burning

Peel and cut potatoes into even 2mm slices using a mandolin or knife

Rinse potatoes with water to remove excess starch and pat dry with a clean towel

Heat 1 liter of sunflower oil in a frying pan to 150°C

Add potatoes to the oil and maintain temperature at 120-130°C for 15-20 minutes, stirring occasionally and allowing some potatoes to break slightly to release starch

Give potatoes a final boost at high heat to create Maillard reactions and crunchiness

Remove potatoes from oil, draining excess oil, yielding approximately 880g cooked potatoes

Beat 12 eggs in a bowl with a spoon, avoiding excess air, until well combined and uniform in color

Combine the cooked potatoes, caramelized onions, and beaten eggs in a bowl

Season with salt to taste (approximately one pinch per egg plus potatoes)

Let the mixture rest for 10 minutes to allow flavors to equilibrate and emulsify

Heat a non-stick pan with a small amount of oil over medium-high heat

Pour the tortilla mixture into the hot pan and cook

Flip the tortilla at least three times during cooking using a plate or tortilla turner to shape it and ensure even cooking

Cook until the exterior is set but the interior remains runny, approximately 8-10 minutes total

Slide onto a serving plate and serve immediately while still warm