How to Make It
Preheat broiler to high with rack 8 inches from heat.
Heat 3 tablespoons of the oil in a medium cast-iron skillet over medium- high. Add potatoes, shallots, 1½ teaspoons of the salt, and 1½ ￼teaspoons of the pepper; cook, stirring often, until potatoes are tender but not browned, 12 to 15 minutes. Transfer to a medium bowl.
Reduce heat to medium-low and add 2 tablespoons of the oil to the skillet. Stir eggs into potato mixture and pour into skillet, pressing into an even layer. Cook, without stirring, until sides and bottom are set and edges begin to pull away from skillet, 8 to 10 minutes.
Transfer to oven and broil until top is set and golden brown, about 3 minutes. Cover skillet with a large plate and carefully invert to release tortilla.
Toss lettuce with 3 teaspoons of the vinegar and remaining 1 tablespoon oil, ½￼ teaspoon salt, and ¼￼ teaspoon pepper.
Combine harissa, sour cream, garlic, and remaining 1 teaspoon vinegar in a small bowl. Cut tortilla into wedges and serve with harissa sauce and salad.