Ingredients

• 3 pounds small white potatoes
• Kosher salt
• 1 cup mayonnaise
• 1/4 cup buttermilk
• 2 tablespoons Dijon mustard
• 2 tablespoons whole-grain mustard
• 1/2 cup chopped fresh dill
• Freshly ground black pepper
• 1/2 cup chopped celery
• 1/2 cup chopped red onion