In a medium (4 quart) pot filled with cold water, bring the whole potatoes to a boil and cook for approximately 20 minutes or until tender but still firm. Drain and place in the refrigerator for at least 1 hour or until cold. Once they’re cold, peel and cut into very thin slices (no larger than 1/8-inch), using either a knife or mandoline. Place the slices in a large bowl and sprinkle with 1/2 teaspoon salt.
Once the potatoes are sliced, add 1 tablespoon olive oil to a large non-stick skillet (10-inch) set over medium-high heat. When the oil is hot, add the diced onion, chorizo and 1/2 teaspoon salt. Sauté for 8 minutes or until the onions have softened and the chorizo has browned. Spoon the mixture over the potatoes and gently fold to combine. Transfer to a large plate and using a rubber spatula form into a 9-inch round disk. Cool, wrap in plastic and place in refrigerator overnight.
The next morning, remove the potatoes from the refrigerator and let stand at room temperature for 30 minutes. In a bowl, beat together the eggs and 1 teaspoon salt.
Heat 2 tablespoons olive oil in a large (10-inch) non-stick skillet, over medium-high heat. When the oil is hot, slide the potato disk into the pan. Using a rubber spatula, flatten the potatoes to fill in any gaps around the edges. Once you’ve created a flat surface, tuck the edges under to create the round shape. Cook for 2 minutes. Make several shallow slits in the top of the potatoes with the spatula and pour the eggs over the top. Scrape the eggs from around the edges and check to make sure that the bottom isn’t sticking (about 2 minutes). Once the tortilla is moving freely in the pan, reduce the temperature to low and cover with a lid. Cook for 16 to 18 minutes. You’re looking for the bottom to be a golden brown and the potatoes on the top to feel warm to the touch. Check around the halfway point to make sure that the tortilla isn’t sticking.
Remove the pan from the heat and place a rimless plate that is slightly larger than the skillet over the top. Using oven mitts or a towel, quickly flip the tortilla onto the plate. Wipe out the skillet with a paper towel to remove any stuck-on bits and return the pan to the stove, raising the temperature to medium. Add the remaining 1/2 tablespoon olive oil and gently slide the tortilla back into the pan. Use the spatula to slide any loose potatoes back under the tortilla. Shake the skillet to make sure that it’s not sticking. Cook for an additional 4 to 5 minutes or until the bottom is golden brown.
Transfer the tortilla to a serving platter and let cool for about 10 minutes before slicing. The tortilla is delicious served warm, at room temperature or cool. Pass around the roasted tomato salsa for topping the tortilla.
It’s important to use potatoes that are similar in shape so that they’ll cook evenly.
If you don’t have a large rimless plate, you can also use either a large rimless cookie sheet or a smooth cutting board. I actually prefer the cutting board since it not only worked well for flipping out the tortilla, but also when transferring it back into the skillet.