How to Make It
Heat a skillet over medium-high. Add 1 tablespoon oil and potatoes; cook 6 minutes. Cover, reduce heat to medium, and cook 6 minutes. Sprinkle potatoes with 1/4 teaspoon salt.
Combine vinegar, mustard seeds, sugar, and 1/4 teaspoon salt in a saucepan; boil. Remove from heat; stir in onion. Let stand 5 minutes. Drain. Stir into potatoes. Top with parsley.