Begin by filling a large bowl with ice water for the ice bath.

In a pot of boiling salted water, add green beans and cook for 3–4 minutes until crisp-tender. Transfer to ice bath.

Using the same water, add the small white potatoes and cook for 15–20 minutes until fork-tender. Let cool slightly.

Whisk together vinegar, mustard, minced garlic, and salt in a small bowl. Gradually add olive oil while whisking to create vinaigrette.

Cut cooled potatoes in half and add to a large mixing bowl. Add drained green beans and vinaigrette. Toss gently to coat.

Garnish with chopped chives and black pepper. Let sit for 15–20 minutes before serving.