2 tablespoons balsamic vinegar
1/4 cup extra-virgin olive oil
1 tablespoon Dijon mustard
2 tablespoons chopped fresh basil
1/2 teaspoon salt
1/4 teaspoon ground black pepper
1/2 cup chopped onion
3/4 cup crumbled blue cheese
2 tablespoons chopped fresh chives
Place potatoes into a large pot and cover with lightly salted water; bring to a boil. Reduce heat to medium-low and simmer until tender, 10 to 15 minutes; drain. Whisk vinegar, olive oil, mustard, basil, salt, and pepper together in a large bowl; add the potatoes and onion. Toss gently to coat. Let stand until cool, about 30 minutes. Fold blue cheese and chives into potato salad until blended.