How to Make It
Preheat broiler with oven rack 3 inches from heat. Place chile on a baking sheet, and broil until charred all over, 6 to 8 minutes, turning once after 3 minutes. Transfer chile to a bowl, cover tightly with plastic wrap, and let stand 5 minutes. Remove and discard charred skin and stem from chile.
Place chile, 2 tablespoons water, and preserved lemon peel and flesh in a blender; pulse until chopped.
With blender running, add egg yolk. Add vegetable oil in a slow, steady stream, processing until mixture thickens. Stir in vinegar and salt. Cover and chill until ready to use, up to 3 days.