Prepare the ice bath by filling a medium bowl with ice water and set aside.

In a large pot, bring salted water to a rolling boil. Add green beans and blanch for 3-4 minutes. Transfer to ice bath.

In the same pot, return the water to a boil, add potatoes, and cook for 15-20 minutes. Drain and cool for 10 minutes before halving.

In a small bowl, whisk together balsamic vinegar, Dijon mustard, minced garlic, and salt. Gradually whisk in olive oil until emulsified.

Combine cooled potatoes and blanched green beans in a large bowl. Pour dressing over and toss gently to coat.

Chop chives and sprinkle over salad, add black pepper to taste, and give it a final gentle toss before serving.