Capers and mustard add tanginess to this creamy salad, while chives, dill and parsley add fresh flavor and a splash of color.
Bring 1 inch of water to a boil in a large saucepan fitted with a steamer basket. Add potatoes, cover and cook until tender, about 15 minutes. Transfer to a baking sheet to cool completely, about 30 minutes.
Meanwhile, whisk mayonnaise, yogurt, lemon juice, mustard, capers, chives, dill, parsley, salt and pepper in a large bowl.
Add the potatoes to the dressing and toss to coat. Add arugula and gently toss again. Garnish with more dill, if desired.