(note: If serving uncooked egg is worrisome, substitute 1/4 cup "Simply Eggs" for the whole egg)
Place egg and cilantro in food processor or blender. Start processing and slowly stream in 1/2 cup of the oil. Add the garlic, 1/2 tesaspoon of the salt and 4 turns of the pepper, stream in the remaining 1/4 cup of the oil. Process until thorougly emulsified into a mayonnaise. Pour the mayonnaise into large bowl and add potatoes, onion and the remaining 1/2 teaspoon salt and 3 turns pepper. Toss to combine thoroughly, cover and refrigerate for up to 24 hours.