Drop potatoes in a large pot of boiling salted water for 20-30 minutes till soft but not too soft. Drain in collander and put a towel over to steam 10 minutes. When you can handle them cut in half and place in a large bowl.
Toss with the white wine and chicken broth allowing the liquid to absorb into potatoes.
Combine vinegar, mustard, 1/2 t salt and 1/4 t of pepper and slowly wisk in olive oil to emulsify. Add to potatoes.
Then add scallions, herbs, 1 1/2 t salt and 1/2 t pepper. Toss and serve warm or at room temperature.