Warm Potato Salad with Goat Cheese

1-2 pounds red potatoes, scrubbed well and cut into 3/4-inch pieces
     
Coarse salt and freshly ground pepper
        
2 tablespoons white-wine vinegar
        
1 teaspoon Dijon mustard
        
3 tablespoons extra-virgin olive oil
       
3 ounces crumbled goat cheese (1/2 cup)
      
1 celery stalk, finely chopped
      
1 small sweet onion, finely chopped
        
2 tablespoons finely chopped fresh flat-leaf parsley
 
    1.    Cover potatoes with water in a medium saucepan; season with salt, and bring to a boil. Reduce heat, and simmer until tender, 10 to 12 minutes. Drain, reserving 1 tablespoon cooking liquid. Let potatoes cool for 5 minutes.
    2.    Whisk together vinegar, mustard, and reserved cooking liquid. Add oil in a slow, steady stream, whisking constantly until emulsified.
    3.    Transfer potatoes to a bowl, and drizzle with vinaigrette. Gently stir in goat cheese, celery, onion, and parsley. Season with salt and pepper.