If you're making your vinaigrette with white-wine vinegar, use 1/2 teaspoon sugar (instead of 1/4 teaspoon) to balance the higher acidity.
•Potatoes can be cooked and tossed with onion and vinaigrette 1 day ahead and chilled, covered. Bring to room temperature (this will take about 1 hour), then add remaining ingredients.
•Green beans can be cooked and celery can be diced 1 day ahead and chilled separately, wrapped well in dampened paper towels, in sealed plastic bags.
Recipe information
Total Time
1 1/2 hr
Yield
Makes 8 servings
Ingredients
Preparation
Step 1
Whisk together vinegar, mustard, pepper, sugar, and 1 teaspoon salt in a small bowl. Add oil in a slow stream, whisking until emulsified.
Step 2
Quarter potatoes, then cover with cold water by 1 inch in a 4- to 5-quart pot and bring to a boil with remaining teaspoon salt. Reduce heat and simmer, uncovered, until potatoes are tender, 8 to 10 minutes. Drain, then transfer hot potatoes to a large bowl and toss with onion and all but 1/4 cup vinaigrette. Cool to room temperature, about 1 hour.
Step 3
While potatoes cool, cook green beans in a 3-quart saucepan of boiling salted water, uncovered, until crisp-tender, 3 to 4 minutes, then drain and transfer to a bowl of ice water to stop cooking. Let stand 2 minutes. Drain and pat dry.
Step 4
Just before serving, toss potato mixture with green beans, celery, parsley, and remaining 1/4 cup vinaigrette.
