green peas, steamed until tender (2 to 5 minutes) if fresh or thawed if frozen
chopped fresh chives
Place the potatoes in a steamer basket fitted over a large pot of boiling water. Cover and steam until the potatoes are knife-tender, 25 to 30 minutes. Remove from the steamer and allow to cool completely. Cut the potatoes into ½-inch cubes.
Place the eggs in a medium pot, cover with water, and bring to a boil. Reduce the heat to medium low and simmer for 9 minutes. Drain and rinse the eggs under cold water, or refrigerate until cool enough to handle, and peel them. Discard 2 yolks and then coarsely chop the remaining eggs.
In a large bowl, whisk together the yogurt, mayonnaise, mustard, vinegar, salt and black pepper. Add the eggs, potatoes, peas and chives and gently fold until combined. Cover and refrigerate to allow the flavors to meld for at least 1 hour and up to overnight.