Warm Potato Salad

Name: Warm Potato Salad
Ingredients: 3 pounds small salad potatoes; 1 onion, finely chopped; 1 teaspoon dijon mustard, or similar; 7 tablespoons white wine vinegar; 300 milliliters beef or vegetable stock; 4 tablespoons vegetable oil; 1/4 bunch chives, finely chopped; salt and pepper, to taste