This may not be the most authentic Spanish omelet, but it's still delicious AF.
Grapeseed oil, for frying
7-8 fingerling potatoes
1 Spanish onion
Grilled green onions
Fill a cast-iron skillet with oil 3/4 of the way up; bring to 350°F.
Cut the fingerling potatoes into 3/4-inch slices; carefully add to hot oil.
While potatoes are frying, slice the onion into 1/8-inch half moons. Crack 12 eggs into a large mixing bowl; beat them with a fork until they are combined.
Once potatoes begin to crisp, add onions to frying pan. Fry onions until they're golden brown. Using a spider tool, remove potatoes and onions from pan and place onto a baking sheet lined with a wire rack to drain. Sprinkle generously with salt and paprika.
Add potato and onion mixture to the bowl with the eggs. Stir with fork to combine.
Remove all but 2 tablespoons of oil from the pan. Pour the egg mixture into the skillet. Use fork to stir while shaking pan until mixture begins to set. Once eggs are no longer runny, use a rubber spatula to form the frittata. Continually move spatula around edges of the pan to loosen. Once the bottom has good color, cover the skillet and invert the frittata out of the pan onto the lid.
Add a little more oil to the skillet if necessary. Slide the frittata back into the skillet cooked-side up, and continue to cook and form those edges with the spatula.
Invert onto a plate when done. Serve with a little mayo or Sriracha and garnish with grilled green onions.