Potatoes:

• 4 sprigs fresh thyme
• 3 sprigs fresh flat-leaf parsley
• 1 sprig fresh rosemary
• 1 bay leaf
• 1 cup dry white wine
• 2 cloves garlic, smashed
• 1/2 pound small, red-skinned potatoes, such as red thumb, scrubbed
• 1/2 pound small, white-skinned waxy-style potatoes, such as German butterball, scrubbed
• 1/2 pound small, blue-potatoes, such as Peruvian fingerling, scrubbed
• 1 tablespoon kosher salt
• 2 stalks celery, thinly sliced

Dressing:

• 1/4 cup white wine vinegar
• 1 tablespoon whole-grain mustard
• 2 teaspoons kosher salt
• Freshly ground black pepper
• 1/2 cup extra-virgin olive oil
• 2 tablespoons minced flat-leaf parsley
• 2 scallions (white and green), thinly sliced