How to Make It
Preheat the oven to 450°. In a large ovenproof nonstick skillet, heat 1/4 cup of the olive oil. Add the onion, potato peels, chopped garlic and all but 1/4 cup of the scallions and cook over moderate heat, stirring occasionally, until golden and crispy in spots, about 10 minutes. In a medium bowl, beat the eggs with the 1/2 teaspoon of pimentón and add to the skillet. Season with salt and pepper and cook over moderately low heat, stirring frequently, until the eggs begin to set around the edges, 3 to 4 minutes. Transfer the skillet to the oven and bake the tortilla for 6 to 8 minutes, until just set.
Meanwhile, in a small bowl, whisk the mayonnaise with the grated garlic, lemon juice and the remaining 6 tablespoons of olive oil; season with salt and pepper.
Invert the tortilla onto a large plate. Garnish with the reserved 1/4 cup of scallions and a sprinkling of pimentón and serve with the garlic aioli.